designing the power train of tamuq formula hybrid in...
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Designing the Power Train of TAMUQ Formula Hybrid in Progress Vehicle
Senior Year Design Project Final Report
Submitted By
Mahmudul Alam Project Lead
Jaber Al-Marri
Team Member
Project Supervisors
Dr. Shehab Ahmed Assistant Professor, Electrical and Computer Engineering
Dr. Mazen Saghir
Associate Professor, Electrical and Computer Engineering
Date of Submission
April 29, 2010
i
Memo To: Dr. Shehab Ahmed, ECEN 405 Instructor and Project Supervisor
From: Mahmudul Alam, Jaber Al-Marri
CC: Dr. Mazen Saghir, Project Co-Supervisor
Date: April 29, 2010
Re: Transmittal Memo
Attached is the final report of our senior year project Designing the Power Train of TAMUQ
Formula Hybrid in Progress Vehicle.
We sincerely believe that this document is an honest appraisal of our project. The report contains
detailed analysis and description of the work that we have done to successfully design and
simulate the whole power train of the electric vehicle. The report also discusses the sporadic
successes we had in product prototyping. At the end, the report identifies the reasons why we
could not achieve some of our project objectives set at the beginning of Fall 2009 semester and
includes recommendations about how those objectives can be achieved.
While writing the report we have always tried to keep our focus on clarity and consistency. We
tried our best to write a report that any senior electrical engineering student studying it should be
able to understand without any confusion and ambiguity.
We have written this report from passive perspective. As for the citation, we have followed IEEE
citation style guide.
Finally, we would like to say that the work that we have done in this project can indeed be an
excellent stepping stone of a project to build a successful motor drive for an electric vehicle
power train that would allow motoring and regeneration both in forward and reverse directions.
ii
ABSTRACT
The objective of this senior design project was to design, simulate, build and test the power train
of an electric vehicle that can participate in 2011 Formula Hybrid Competition. The project
consisted of three major tasks: motor sizing, motor controller designing, and battery sizing. The
traction motor was sized such than it can supply power that is greater than the power required by
the vehicle to achieve the minimal acceleration specified in the contest rule book. After selecting
the motor, the vehicle acceleration performance for the chosen motor was simulated using
MATLAB. As for the motor controller, it had two parts: (i) the power stage circuit, which was
basically a power electronic converter (ii) the control circuit. A full bridge four quadrant
topology was chosen as the topology of the power electronic converter to facilitate motoring and
regeneration both in forward and reverse directions. As for the converter controller, digital
control method was preferred over analog control method because of design ease. The digital
control was realized through a micro-controller. The motor controller features include LCD
display, speed limiting, current limiting, ripple filter pre-charge, automatic shutdown, various
fault detections and some EMI/noise immunity measures. The whole control circuit and the
firmware written for it were simulated in PROTEUS VSM software.
As for the battery sizing, only preliminary literature survey could be done. Although the motor
controller design and simulation were successful, the prototype controller could not be built due
to time constraint and unavailability of an in-circuit programmer.
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Table of Contents
Transmittal Memo .....................................................................................................................i Abstract .................................................................................................................................... ii Table of Contents .................................................................................................................... iii List of Figures............................................................................................................................ v List of Tables ...........................................................................................................................vii Glossary ................................................................................................................................. viii Acknowledgement .................................................................................................................... ix Chapter 1 Introduction ........................................................................................................... 1
1.1 Introduction ..................................................................................................................... 2 1.2 Need Statement ................................................................................................................ 2 1.3 Background and Conceptual Analysis .............................................................................. 3 1.4 Function Structure and Functional Decomposition ........................................................... 7 1.4 Design Specifications ....................................................................................................... 8 1.6 Outline of the Report........................................................................................................ 9
Chapter 2 Motor Sizing and Acceleration Simulation ......................................................... 11 2.1 Permanent Magnet DC Motor ........................................................................................ 12 2.2 Why Permanent Magnet DC Motor ................................................................................ 15 2.3 Initial Order of Magnitude Calculation ........................................................................... 16 2.4 Chosen Motor and its Technical Specifications .............................................................. 21 2.5 Performance Simulation of TAMUQ HIPV for the Chosen Motor ................................. 22
Chapter 3 Power Stage Circuit Design ................................................................................. 25 3.1 Converter Type .............................................................................................................. 26 3.1 Converter Topology Selection ........................................................................................ 26 3.3 Semiconductor Switch Realization ................................................................................. 31 3.4 Gate Drive Circuit .......................................................................................................... 34 3.3 Pre-Charge Circuit ......................................................................................................... 37
Chapter 4 Control Circuit Design ........................................................................................ 39
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4.1 Micro-controller Interfacing with Accelerator and Brake ............................................... 40 4.2 Current Limiting Circuit ................................................................................................ 42 4.3 Speed Limiting Circuit ................................................................................................... 44 4.4 Battery Voltage and Power Stage Voltage Feedback ...................................................... 47 4.5 Power Supply for Gate Drive and other ICs.................................................................... 48 4.6 Shoot-Through Protection Logic .................................................................................... 49 4.7 EMC Considerations ...................................................................................................... 50
Chapter 5 Micro-Controller Module, Firmware Development, & Firmware Simulation . 55
5.1 Digital vs. Analog Control ............................................................................................. 56 5.2 About the Chosen Micro-controller ................................................................................ 56 5.3 Program Algorithm ........................................................................................................ 58 5.4 Firmware Development .................................................................................................. 61 5.5 Firmware Simulation...................................................................................................... 65
Chapter 6 Battery Sizing ...................................................................................................... 70 6.1 Importance of Battery in Electric Vehicles ..................................................................... 71 6.2 Important Battery Parameters ......................................................................................... 71 6.3 Need Analysis of TAMUQ HIPV Battery Pack .............................................................. 74 6.4 Chemistry of the Chosen Battery .................................................................................... 76
Chapter 7 Conclusion ........................................................................................................... 77
7.1 Project Achievements/Incompleteness ........................................................................... 78 7.2 Future Work Recommendations ..................................................................................... 81
Works Cited ........................................................................................................................... 82 Appendix 1. Project Management and Earned Value Spreadsheet ...................................... 86 Appendix 2. Acceleration Simulation MATLAB Code .......................................................... 90 Appendix 3. Firmware Code ................................................................................................... 91 Appendix 4. Circuit Diagram ................................................................................................. 96 Appendix 5. Bill of Materials .................................................................................................. 98 Appendix 6. Filter Inductor and Capacitor Selection Calculations .................................... 100 Appendix 7. Report Attachment ........................................................................................... 116 Appendix 8. Student Biography............................................................................................ 117
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List of Figures
Figure 1.1 Conceptual illustration of TAMUQ HIPV power train.
Figure 1.2 Conceptual illustration of the DC traction motor controller.
Figure 1.3a Fundamental function structure of the drive train.
Figure 1.3b Sub-function structures of block 2.
Figure 1.3c Sub-function structures of block 4.
Figure 1.3d Sub-function structures of block 5.
Figure 2.1a Basic configuration of a permanent motor.
Figure 2.1b Left hand rule.
Figure 2.2 Torque-Speed characteristics of a permanent magnet motor.
Figure 2.3 The free body diagram showing the forces acting on the vehicle going up on a slope.
Figure 2.4 The Mars ME-0708 PM Pancake Brushed AKA Etek-R motor.
Figure 2.5 Simple TAMUQ HIPV drive train arrangement.
Figure 2.6 Speed of the TAMUQ HIPV for the chosen motor.
Figure 3.1a Full bridge 4-quadrant converter topology.
Figure 3.1b Quadrants of operation.
Figure 3.2a Step a operation.
Figure 3.2b Step b operation.
Figure 3.2c Step c operation.
Figure 3.2d Step d operation.
Figure 3.3 Switching sequence (iG1, iG2, iG3, iG4), output voltage (Vld), load current (ild), and
battery current (iB) waveforms during mode 1 operation.
Figure 3.4 Switching sequence (iG1, iG2, iG3, iG4), output voltage (Vld), load current (ild), and
battery current (iB) waveforms during mode 2 operation.
Figure 3.5 Semiconductor switching loss during motoring.
Figure 3.6 Simplified MOSFET Model showing parasitic components.
Figure 3.7 Gate voltage vs. total gate charge graph for the chosen MOSFET.
Figure 3.8 Gate drive circuit.
Figure 3.9a High inrush current and its exponential decay.
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Figure 3.9b The pre-charge circuit designed for TAMUQ HIPV power train.
Figure 4.1 The acceleration pedal.
Figure 4.2 Interfacing the MCU with the APPS.
Figure 4.3 The brake circuit.
Figure 4.4 Hall Effect.
Figure 4.5a Hall sensing method.
Figure 4.5b Chosen Hall sensor connection diagram.
Figure 4.6 The chosen incremental encoder.
Figure 4.7 Speed limiting circuit-encoder and frequency to voltage converter.
Figure 4.8 Power stage and battery voltage feedback.
Figure 4.9 Power supply circuitry.
Figure 4.10 Left side and right side MOSFET half bridges.
Figure 4.11 Shoot-through protection logic scheme.
Figure 4.12a Graph to determine initial current and damping factor.
Figure 4.12b Snubber circuit.
Figure 4.13 RC filter circuits for feedbacks.
Figure 5.1 Analog to digital conversion.
Figure 5.2a Direction check sub-routine.
Figure 5.2b System shutdown sub-routine.
Figure 5.3 The big loop.
Figure 5.4 Configuration bits.
Figure 5.5 The circuit used to simulate the firmware in Proteus VSM.
Figure 6.1 Approximate representation of a traction battery cell.
Figure 7.1 Micro-controller pedal interfacing.
Figure 7.2 Encoder testing.
Figure 7.3 Current sensor testing.
Figure 7.4 The PICStartPlus Programmer.
Figure 7.5 Product prototype.
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List of Tables
Table 1.1 Drive train design specifications.
Table 2.1 Estimation of parameters required to calculate the total tractive force.
Table 5.1 ADCON1 register configuration bits.
Table 5.2 Micro-controller pin assignments.
Table 5.3 Drive parameters and Scaling Factors.
Table 5.4 Step by step explanation of firmware simulation.
Table 6.1 TAMUQ HIP Vehicle battery pack needs/constraints specifications.
Table 6.2 Comparison between Thundersky, Optima Red-Top and Valence batteries.
viii
Glossary
AC Alternating Current
APPS Acceleration Pedal Position Sensor
BJT Bipolar Junction Transistors
DC Direct Current
DIP Dual In-line Package
DOD Depth of Discharge
DPDT Double Pole Double Throw
EEPROM Electronically Erasable Programmable Read Only Memory
EMC Electromagnetic Compatibility
EMI Electromagnetic Interference
HIPV Hybrid in Progress Vehicle
HV Hybrid Vehicle
IEEE Institute of Electrical and Electronics Engineering
LCD Liquid Crystal Display
MMF Magnetomotive Force
MOSFET Metal Oxide Semiconductor Field Effect Transistor
PCB Printed Circuit Board
PWM Pulse Width Modulation
RISC Reduced Instruction Set Computer
SAE Society of Automotive Engineers
SCR Silicon Controlled Rectifiers
SOA Safe Operating Area
SOIC Small Outline Integrated Circuit
SPST Single Pole Single Throw
WOT Wide Open Throttle
ix
Acknowledgements
We first of all express our humble gratitude to the Almighty Allah, the Creator and the Sustainer
of this universe, the Knower of the seen and unseen, for all that we have achieved through
working in this project that spanned from Fall 2009 to Spring 2010 semester.
We thank our project supervisors, namely Dr. Shehab Ahmed and Dr. Mazen Saghir. Dr. Mazen
taught us the Microprocessor System Design (ECEN 448) course whereas Dr. Shehab taught us
the Power Electronics (ECEN 438) course and guided us the though the project by teaching
Preparation for Senior Year Design (ECEN 489) and Senior Design (ECEN 405) courses. The
concepts learned in these courses, especially the learn-by-design approach followed by Dr.
Shehab in his Power Electronics course, were very helpful in designing and simulating the
microcontroller based motor drive. Apart from teaching, both Drs. Shehab and Mazen met with
us every week, reviewed our weekly reports, answered our questions and provided us with their
valuable feedbacks.
In addition, we also thank our workshop technician Engineer Abdallah Al-Mardawi, who
carefully went through our bill of materials and processed the order. As part of the ECEN 489
course, he taught us the use of Multisim and Ultiboard software. It was his idea to use the
concept of Whitestone Bridge in the circuit that interfaced the micro-controller unit with the
acceleration pedal. He also manufactured the printed circuit board (PCB) of the low power
control circuit module and helped us building the power stage circuit.
We are also grateful to Lab Engineers Mr. Wesam Mansour and Mr. Kais, who have provided us
with some of our required power electronic components from their respective lab. Aside from it,
whenever we have approached them to discuss anything pertaining to our project that we thought
they could help, they have never disappointed us and despite being busy, they have always
welcomed us with a smile and tried their best to help us. Their unquestionable work ethic will
always be a model for us and we again say to them “Thank You”.
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Last but not least, we would like to thank our family members, especially our parents, whose
inspiring words kept our work-spirit enlivened during times when get going was tough. We
forever owe to them for this psychological support, which was extremely necessary in seeing
through the challenging phases of the project.
1
CHAPTER 1
INTRODUCTION
_______________________
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1.1 Introduction
As the non-renewable sources of energy are shrinking and concerns over environmental pollution
are growing everyday due to increasing use of fossil fuels, the focus of the automotive industry
has shifted to making unconventional vehicles like hybrid vehicles and electric vehicles that are
more energy efficient and have lower green house gas emission rate. In order to motivate
students and make them more involved in the research of hybrid and electric vehicle technology
and bring out new ideas from them, the Thayer School of Engineering of the Dartmouth College,
USA, organizes a racing competition each year where formula shaped Hybrid Vehicles (HV) and
Hybrid in Progress Vehicles (HIPV) designed and fabricated by undergraduate and graduate
students of participating universities compete against each other. The competition terms electric
vehicles as HIPVs. The event is sponsored by the Institute of Electrical and Electronics
Engineering (IEEE) and the Society of Automotive Engineers (SAE). The Electrical and
Mechanical Engineering department of Texas A&M University at Qatar (TAMUQ) had decided
to build a HIPV to participate in the 2011 Formula SAE competition. This is a two year project.
The class of 2010 mechanical engineers focused on designing and simulating the chassis, the
brake and the steering system whereas the electrical engineers focused on designing, simulating,
building and testing a prototype power train. This report presents a detailed description of all the
steps of the prototype power train design, simulation, and fabrication.
1.2 Need Statement (applicable only for electrical engineering team)
“Design, simulate, build, and test a prototype power train of the HIPV that is capable of
propelling the car by means of a traction motor powered from its onboard batteries. The power
train should meet the minimum performance requirements and abide by all the rules and
regulations stipulated in the Formula Hybrid Competition 2010 rule book.”
3
1.3 Background and Conceptual Analysis
The power train of any auto-mobile can be defined as a sub-system that generates power and
then converts it into mechanical power to propel the vehicle. A simple battery electric vehicle
like the TAMUQ HIPV can have a power train configuration like the one shown below in Figure
1.1.
Figure 1.1 Conceptual illustration of TAMUQ HIPV power train [1].
The power train system shown in Figure 1.1 is actually comprised of three major sub-systems:
the traction motor, the motor controller, and the energy source unit.
The Traction Motor: The traction electric motor is the center of any electric vehicle propulsion
system. Selecting a motor of appropriate type and rating is very important. The electrical
engineers thus focused on sizing a DC motor such that it would meet all the performance
requirements. To keep the power train design simple, it was decided that the gearing would be
kept fixed. The traction motor and the fixed gearing would then be put together in a single
package with both ends of the axles pointing towards the driving wheels [2].
The Motor Controller: The controller acts like a central processing unit of an electric vehicle as it
co-ordinates among the driver, the traction motor and the energy source unit. Depending on the
Fixed gearing
4
throttle and the brake input from the driver, the controller determines the speed and the torque of
the traction motor by regulating the power supply from the energy source unit. The electrical
team decided to design and fabricate a motor controller instead of buying a commercial one. The
motivation behind such approach was:
At the beginning of Fall 2009 semester, a meeting was organized between the electrical
and the mechanical engineers (including the professors) to determine the project
expectations. It was unanimously decided that given the resources available at TAMUQ,
fabricating a whole car would not be possible in a year. Thus the TAMUQ HIPV
electrical team took this first year of the project as an opportunity to design and fabricate
a motor controller of their own so that they can have a product prototype to display on the
demo day.
The commercial motor controllers available from Curtis Instruments and other such
companies are usually one or two quadrant motor controller and do not provide with
regenerative breaking option. The Texas A&M University (College Station) Formula
Hybrid Team, who won the first place in 2009 Formula Hybrid Competition, also used a
motor controller that had no regenerative breaking option. This motivated TAMUQ
students to design a motor controller that would incorporate four quadrant full bridge
topology and allow motoring and regenerating both in forward and reverse directions.
The commercial motor controllers are very expensive. A typical programmable DC motor
controller from Curtis costs about thousand US dollars. The economical solution
therefore was to build our own controller.
A conceptual illustration of the DC traction motor controller design is shown in Figure 1.2.
5
Figure 1.2 Conceptual illustration of the DC traction motor controller.
The motor controller to be designed was a micro-controller based solid-state type controller. As
seen from Figure 1.2, the power stage contains the MOSFET H-bridge, current and voltage
ripple filter, and the traction motor. The low power control circuit includes a micro-controller, an
LCD screen, and gate drive ICs. Based on the pulse width modulated (PWM) signal generated by
the micro-controller, the gate drive circuit will command the state of the semi-conductor
switches in power stage circuit, which in turn will regulate the power to be supplied from the
battery to the traction motor [3]. The duty ratio of the PWM signals will depend on the brake and
accelerator input from the driver. This controller therefore is essentially a DC-DC converter as it
uses the PWM signal to chop the input voltage and deliver the desired voltage to the load. The
output filter will lessen the ripple of the load current and the LCD will notify the driver about the
driving mode and display other necessary information.
The Formula Hybrid 2010 Competition rules strongly suggest the students to use commercially
available motor controllers, mainly because of their safety and reliability. Also the commercial
motor controllers are manufactured as per IEEE standards. A motor controller built in the lab
surely will not have the reliability and safety measures as much as that of commercial ones, but
effort was made nonetheless to include as many protection schemes in the custom built motor
controller of TAMUQ HIPV. The protection/safety measures that were decided to be included
are:
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Over voltage protection.
Under voltage protection.
Current limiting
o Different current limit for forward motoring, reverse motoring and regeneration.
Speed Limiting
o Different speed limit for forward and reverse mode.
Fault detections
o Motor direction will not be changed (if direction switch is changed accidentally)
until the speed is zero.
o Power stage will not be on if the pre-charge capacitor is not fully charged.
o Brake overrides accelerator.
o Preventing shoot-through of MOSFETs.
o No regeneration if the battery voltage is more that 75% of its nominal voltage.
o A switch to instantly turn off power stage if something goes wrong.
o Automatic system shutdown if any of those faults are detected.
Electromagnetic Compatibility (EMC).
All these protections and fault detection measures are discussed in detail later in the report.
When the car shall be built in 2011, the students will have two options: (i) either buy a new
commercial motor controller, or, (ii) improve the motor controller built by 2010 electrical
engineers by incorporating more safety features and re-build it.
The Energy Source Unit: For a battery electric vehicle like TAMUQ HIPV, the energy source
unit will mainly include banks of deep cycle rechargeable batteries and a battery charger.
Although the prototype power train was decided to have voltage supply from DC supply units
available in Dr. Shehab’s lab, the students however did a literature survey on electric vehicle
batteries and dedicated a chapter of this report on battery sizing.
7
1.4 Function Structure and Functional Requirements
Based on the discussion in Section 1.3, a comprehensive function structure of the whole power
train system was developed. Figure 1.3a - Figure 1.3d illustrate the function structure. Any
functional block, be it a main block or a sub-functional block, includes three items: block
number, title of the block (usually the design feature) and the functional requirement of that
respective block.
Drive Train ofTAMUQ Formula HIP Vehicle
2.Motor Drive: PMT control the
speed of the motor.
1. Electric Motor: PMT propel the vehicle forward.
3. Battery: PMT power generation.
4. Ancillary Systems
5. PMT Electrical Safety
Figure 1.3a Fundamental function structure of the drive train.
Figure 1.3b Sub-function structures of block 2.
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Figure 1.3c Sub-function structures of block 4.
Figure 1.3d Sub-function structures of block 5.
1.5 Design Specifications
Table 1.1 summarizes the design features, the design parameters, and the performance requirements of each of all the functional blocks identified in section 1.4.
Table 1.1 Drive train design specifications.
Block
Design Feature
Design Parameter Performance Requirements
1 Electric Motor
power, speed, torque, current,
efficiency
Covering 75 meters in less than 10 seconds (Minimum 54 kph after 10 seconds starting from zero initial
speed). [4]
2.1.1 Throttle Voltage 5V = Wide open throttle, 0 V = Idle. 2.1.2 Brake Voltage 5V = Wide open throttle, 0 V = Idle.
2.1.3 Voltage Divider Voltage 5V = Pre-charge capacitor voltage close to battery voltage, 0 V
= otherwise.
2.1.4 Voltage Divider Voltage 5V = Battery voltage 48V, 0 V = Battery voltage 0.
2.1.5 Tachometer Voltage 5V = Maximum allowed speed, 0 V = Rest.
2.1.6 Current Sensor Voltage 5V = Maximum positive current, 2.5 V = 0 current, 0 V`=
maximum negative current.
2.1.7 Switch On/Off On`= power stage enable/forward, Off = power stage disable/reverse.
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2.2.1 MOSFET Bridge Topology Full bridge four quadrant topology.
2.2.2 Filter Volt, Ampere Throw voltage ripple = 1 V.
Load current ripple = 3% of load current. Load voltage ripple = 5mV.
3 Battery Volt Maximum voltage 48 V when charged.
4.1 Brake Light Power Power consumption 15 W, clear visibility between wheel centerline and driver shoulder level. [5]
4.2 Speedo Meter Km/h Accurate reading up to 1 place after the decimal.
4.3 Voltmeter V Accurate reading up to 2 places after the decimal.
4.4 Master Switch time 1s
4.5 Warning Strobe Light SAE standard SAE standard J1318 Class 3 [6]
4.6 Transponder NA AMB TranX260 (rechargeable/direct power). [7]
5.1 High
Voltage Isolation
NA Vehicle frame isolation from any part of HV circuit, separation of HV and LV circuits. [8]
5.2 Ground Fault
Detector NA Bender IR486 or IR475LY or equivalent. [9]
5.3 Water proofing
Vehicle should survive a 60s water spray test with all systems energized, without tipping ground fault detector. [10]
5.4 Wiring IEEE standards
No connection exposure, insulation materials rated for maximum expected temperatures, HV wiring done according to
professional standards, non-conductive conduit should be electri-flex LNMP or equivalent, exposed conductive objects
need be grounded. [11]
5.5 Fuse Volt, Ampere
HV and LV circuits should be fused; continuous current rating of the fuse must be smaller than current rating of the element it protects; fuses must be rated for highest voltage in the systems
they protect. [12]
1.6 Outline of the Report
Chapter 1 introduces the project, defines the need statement and gives an overview of the whole
project though background discussion and conceptual analysis. It then focuses on the
development of the function structure, functional requirements and design specifications of the
project.
Chapter 2 is dedicated on sizing a suitable traction motor for the power train. This chapter
elaborates on the benefits of using a permanent magnet motor, principles of operation of a
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permanent magnet motor, initial order of magnitude calculations, and vehicle acceleration
simulation for the chosen motor.
Chapter 3 contains the power stage circuit design in detail. It discusses the reason for choosing
four quadrants full bridge topology and sheds light on the switching sequences of power switches
to achieve all four quadrants of operation. It then talks about the power semiconductor
realization of the converter topology, chosen MOSFET salient properties, heat sink requirements,
gate drive design issues and pre-charge circuit design.
Chapter 4 offers detailed discussion on the low power control circuit module. It covers design
and testing of power supply circuits, microcontroller-accelerator interfacing circuit, current sense
circuit, motor speed feedback circuit, voltage dividers, and LCD display. This chapter also
describes the protection/fault detection measures and EMC issues in detail.
Chapter 5 discusses the firmware development of micro-controller and simulation of its
firmware. The chapter also details about digital control of motors, micro-controller programmer,
firmware algorithm and code writing.
Chapter 6 presents the literature survey about battery types of electric vehicle, battery sizing
procedure, costs and benefits of different types of batteries and battery charging system.
Chapter 7 is the concluding chapter. This chapter summarizes the achievement of this project,
discusses why some of the objectives could not be achieved, and includes recommendations
about how the whole motor controller could be improved if someone again undertakes this
project and tries to rebuild it in future.
11
CHAPTER 2
MOTOR SIZING & ACCELERATION
SIMULATION
________________________________________
12
The most crucial part of any electric vehicle propulsion system is the traction motor. It is the
motor that converts the electrical energy into mechanical energy. The objective of motor sizing
was to select a traction motor that can well meet the performance requirements set in the
Formula SAE Rules. For the TAMUQ HIPV, a permanent magnet DC motor was chosen as the
motor type. In sizing the motor, the total tractive force required to move the vehicle forward was
first calculated. Then the power required to accelerate the vehicle to 15 m/s in less than 10
seconds starting from rest, and the power required to drive at a constant speed were determined.
Based on this initial order of power magnitude calculation, a motor was chosen such that it can
supply power that is well above the power required for either acceleration or constant speed
cruising. Finally a MATLAB program simulated the performance of the TAMUQ HIPV for the
chosen motor.
2.1 Permanent Magnet DC Motor
2.1.1 Principles of Operation
Any brushed DC electric motor consists of a stationary part called stator and a rotating part
called rotor. Magnetic fields are created both in the stator and the rotor of the motor. Through the
interactions between the stator magnetic field and rotor magnetic field, motion is created. There
are two ways a stator magnetic field can be created: using either a permanent magnet or an
external field circuit. In a permanent magnet DC motor, a permanent magnet is used as the stator.
For the rotor or armature magnetic field, a current carrying conductor loop is used. According to
the theory of electricity and magnetism, if a current carrying loop is placed in a magnetic field,
the loop will experience a force exertion on it. The direction of the force is determined according
to Fleming’s Left hand Rule. A permanent magnet DC motor utilizes that principle. The basic
configuration of a permanent magnet DC motor is shown in Figure 2.1a and Fleming’s Left
Hand Rule is shown in Figure 2.1b.
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Figure 2.1a Basic configuration of a permanent motor [13]. Figure 2.1b Left hand rule [14].
In the simplified configuration illustrated in Figure 2.1a, the current path is brush X-commutator
A-coil-commutator B-brush Y. As per the Left Hand Rule, the loop leg that is closed to the north
pole of the magnet is experiencing a force in upward direction whereas the loop leg that is closed
to the south pole of the magnet is experiencing a force in downward direction. These two
opposing forces cause the current carrying loop along with the commutators to rotate. The
rotational momentum causes the loop rotate until commutator B is connected with brush X and
commutator A is connected with brush Y. Despite the current path being changed from XABY to
XBAY, the direction of the current flow remains same and the motor thus keeps rotating in a
constant direction.
2.1.2 Torque-Speed Characteristics
The torque of a permanent magnet motor is specified by:
nrBIlTmotor 2 (2.1) Here n is the number of turns in the armature coil, B is the magnetic field, l is the length of the
coil and I is the current flowing in the armature. This equation could be re-written as follows:
14
]max[]2[armaturethethroughgoingfluxABInT
coilarmaturetheofareatherlnABIT
motor
motor
IKT mmotor (2.2)
Here mK is the construction coefficient of motor that depends on n and many other factors.
Equation 2.2 shows that the motor torque is directly proportional to the armature current and
armature current is dependent on supply voltage sE .
Since the current carrying armature will be rotating in a magnetic field, there will be a voltage
induced in it, which can be expressed as follows:
][2 rvBlrnnBlvEb (2.3)
This is known as the back EMF. In Equation 2.3, factor of 2 appears because the armature has
two sides, each of length r.
Therefore, the current flowing in the armature circuit is:
a
m
a
s
a
bs
RK
RE
REEI
(2.4)
Here aR is the armature resistance. This equation suggests that back EMF is zero when the
speed of the motor is zero and consequently, the armature current during motor starting will be
very high. When load is increased, the speed will drop and so will the back EMF and armature
current.
Inserting Equation 2.4 into the Equation 2.2 we get:
kTR
KR
EKT
a
m
a
sm 0
2)( (2.5)
Here a
sm
REKT
0 anda
m
RK
k2)(
. This equation shows that permanent magnet motor torque is
linearly related with the angular velocity. This torque-speed relationship is illustrated in Figure
2.2.
15
Figure 2.2 Torque-Speed characteristics of a permanent magnet motor [15].
Figure 2.2 shows that permanent magnet motor gives high starting torque, a necessary criterion
of a traction motor.
2.2 Why Permanent Magnet DC Motor
Most commonly used traction motors for electric vehicles are series DC motor, AC induction
motor or permanent magnet synchronous motor. However, for this project a permanent magnet
DC motor was chosen mainly because its linear torque speed characteristics [13], which makes
the design of the power electronic controller simple. Some other benefits that permanent magnet
motors provide are listed below:
Since the flux is produced by the permanent magnet, there is no need for external flux
control circuit.
Because of having no field circuit, the permanent magnet motor does not have any field
copper losses like shunt DC motors [16].
16
Since no field windings are required, permanent magnet motors are smaller in size
compared to shunt DC motors [17].
Permanent magnet motor does not provide as high starting torque as that of a series DC
motor; it nonetheless provides a high starting torque.
Unlike AC induction motor, permanent magnet motor does not require inverter circuitry
to convert vehicle on board DC supply into AC and it saves cost.
A major disadvantage of a brushed permanent magnet motor is the loss that occurs in its brushes
and commutators through sparking. Because of sparking, brushes and commutators wear out
over time and they therefore require periodic maintenance.
Another two disadvantages of a permanent magnet motor are its low torque inducement and
armature reaction effect. A permanent magnet cannot produce magnetic flux density that is as
high as that of an external field circuit. As a result, the induced torque on the armature of a
permanent magnet motor is lower than the induced torque on the armature of a shunt DC motor
for the same amount of armature current. The armature reaction effect may demagnetize the
motor. The current in the armature produces its own magneto-motive force (mmf) and the net
mmf of the machine is the difference between the mmf of the magnetic poles and the mmf of the
armature. If the armature current is too high, it may completely “demagnetize the poles,
permanently reducing and re-orienting the residual flux in them” [18].
2.3 Initial Order of Magnitude Calculation 2.3.1 Total Tractive Force [19]
a. Rolling Resistance Force: The force required to overcome the friction of the tires on the
drive track is called rolling resistance force. If the car is driven on a hard surface, the
rolling resistance arises due to the deflection of tire materials. If the track surface is soft
compared to the tire material, the deformation of the track surface cause the rolling
resistance. Normally rolling resistance is independent of the vehicle speed and is
proportional to the vehicle weight. Equation 2.6 gives the rolling resistance force.
17
mgF rrrr (2.6)
Here rr is the coefficient of rolling resistance and m is the mass of the vehicle.
b. Aero-Dynamic Drag Force: This force helps the vehicle to counteract the friction that
works against it due to cruising through the air. The formula of aero dynamic drag force
is given in Equation 2.7.
)1(21 2
Wdad CvACF (2.7)
Here is density of the air, v is the velocity of the car relative to the air, A is the vehicle
frontal area, dC is the drag coefficient, and WC is the wind speed co-efficient.
c. Uphill Grading Force: When moving through a slope, a component of the vehicle weight
produces a force that opposes the forward motion while ascending. In vehicle
acceleration simulation, only the uphill grading force is taken into consideration. The
uphill grading force acting on a car going up on a ramp is given in Equation 2.8.
)sin( mgFhc (2.8)
Figure 2.3 The free body diagram showing the forces acting on the vehicle going up on
a slope [20].
d. Linear Acceleration Force: Linear acceleration can be found straightforward from
Newton’s second law of motion:
18
maFla (2.9)
Here a is the linear acceleration of the car.
e. Angular Acceleration Force: The force that supplies the angular acceleration can be
formulated as follows:
2
2
raGIF
gwa
(2.10)
Here G is the gear box ratio, g is the gear box efficiency, I is the moment of inertia of
the electric motor, and r is the radius of tire. However, there are no easy ways to calculate
the moment of inertia of an electric motor and the quantity is not specified in most motor
datasheets either. Thus as an expedient measure, the angular acceleration force is
excluded from total tractive force and to compensate this exclusion, the mass in the linear
acceleration force is multiplied by a mass factor called , which increases the mass by
5%.
The sum of all the forces given in Equation 2.6, 2.7, 2.8, 2.9 gives the total tractive force.
ammgCvACmgF
FFFFF
Wdrrtractive
lahcadrrtractive
)sin()1(21 2 (2.11)
2.3.2 Determination of Minimum Tractive Power Requirement
The power required by the car when it is accelerating can be found by dividing its final kinetic
energy by acceleration time span. Mathematically it is expressed as follows:
2)(21
fa
a vmt
P (2.12)
As specified in the SAE Formula Hybrid Competition rules, the minimum performance
requirement for any car entering the contest is completing 75 meters in less than 10 seconds,
19
which translates into accelerating at 1.5 m/s2 starting from rest and achieving a final speed of 15
m/s after 10 seconds. Assuming the mass of the car is 500 kg, the power required for this
acceleration phase is:
kWPa 625.5)15(500)10(2
1 2
A different amount of energy will be required when the car stops accelerating and starts cursing
at a constant speed. Power required for cursing at a constant speed is the product of total tractive
force defined in equation 2.11 and speed.
vFP tractiveC (2.13)
Table 2.1 presents a reasonable estimation of the parameters that are needed to calculate the total
tractive force.
Table 2.1 Estimation of parameters required to calculate the total tractive force.
Quantity and Unit Symbol Estimated
Value Comment
Rolling Resistance
Coefficient (NA) rr 0.075
Specially designed EV tyre has smaller
rolling resistance coefficient
Vehicle Weight (kg) m 500
It is expected that TAMUQ HIP will
weigh lower than 500 kg.
Gravitational Constant
(m/s2)
g 9.8
Density of Air (kg/m3) 1.25
Depends on altitude, temperature and
humidity.
Aero-Dynamic Drag Cd 0.4
20
Coefficient (NA) Depends on vehicle design; with good
design it is possible to lower drag
coefficient to 0.19.
Frontal Area (m2) A 1
Formula shape of the car helps reduce
the frontal area.
Wind Speed Coefficient
(NA)
CW 0.2
Road Angle (rad) 0
Assuming the drive track is not tilted.
Gear Ratio (NA) G 2:1
Mass Factor (NA) 1.05
Compensate the exclusion of angular
force from total tractive force
calculation by increasing the mass of the
linear acceleration by 5%
Tyre Radius (m) r 0.25
If the TAMUQ HIPV cruise at a speed of 15 m/s or equivalently at 54 kph, which is the
minimum final speed the car is required to achieve after the initial acceleration phase, then the
power required to cruise at this speed is:
kW
vammgCvACmgvFP WdrrtractiveC
525.6150015)2.01(4.0125.15.08.9500075.0
)sin()1(21
2
2
Comparing the power required for acceleration phase and constant velocity phase, it can be
concluded that TAMUQ HIP needs a motor that can supply power more than 6.5 kW.
21
2.4 Chosen Motor and its Technical Specification
The initial order of magnitude calculation suggested that the TAMUQ HIP vehicle needs a
traction motor of at least 6.5 kW power to achieve the minimum performance requirement.
However, this initial order of magnitude calculation was done mostly by approximating the
parameters that impact the tractive force. Those parameters will vary depending on track surface,
vehicle weight, temperature, humidity, chassis design, angle of track, and motor moment of
inertia. Additionally to win the acceleration event and endurance event, the car will have to
produce performance better than the specified minimum performance. The chosen motor was
Mars ME-0708 PM Pancake Brushed AKA Etek-R. The motor can produce a rated output power
of 4.5 kW, which means two motor will have to be used for the HIPV power train. The nominal
voltage and current rating of the motor is 48 V and 100 A, respectively. A picture of the motor is
given in Figure 2.4.
Figure 2.4 The Mars ME-0708 PM Pancake Brushed AKA Etek-R motor [21].
In 2009 Formula Hybrid Competition, two participating university’s HIVs used the same type of
motor. They were McGill University and Drexel University.
22
2.5 Performance Simulation of the TAMUQ HIPV for the Chosen Motor [22] The key to vehicle acceleration simulation is to build up a dynamic equation that describes the
velocity and acceleration of the vehicle at any instant. The first step towards building this
dynamic equation is to find the total tractive force that propels the vehicle forward. This has
already been done in section 2.3. To get the dynamic equation, the LHS of Equation 2.11 needs
to be connected with the torque of the chosen motor.
Since there will be no clutch and the car will have a fixed gearing, the drive train will be very
simple. The electric motor, the fixed gearing and the differential will be integrated into a single
assembly. Therefore the LHS of Equation 2.11, the total tractive force exerted by the power
train, can be found from a simple analysis of the drive train arrangement, shown in Figure 2.5.
Figure 2.5 Simple TAMUQ HIPV drive train arrangement.
From the free body diagram shown in Figure 2.5, it is obvious that the axle torque is the product
of the tractive force and the tire radius. Rearranging, total tractive force could be written as:
tractivetractivetractiveaxle rFrFFrT )90sin(
rT
Gr
TF motoraxle
tractive (2.14)
Inserting the motor torque expression from Equation 2.5, Equation 2. 14 becomes:
)()( 00 rvkGT
rGkT
rGFtractive (2.15)
23
Inserting the RHS of Equation 2.15 to the LHS of Equation 2.11, we get:
m
mgCvACmgrvkGT
rG
dtdv
ammgCvACmgrvkGT
rG
Wdrr
Wdrr
)sin()1(21)(
)sin()1(21)(
20
20
(2.16)
Equation 2.16 is the differential equation that governs the speed of the motor at any time. For the
parameters estimated in Table 2.1 and the motor technical specification taken from its datasheet,
the TAMUQ HIPV acceleration performance was simulated by MATLAB and is shown in
Figure 2.6.
Figure 2.6 Speed of the TAMUQ HIPV for the chosen motor.
Figure 2.6 shows that the lesser the weight of the car, the quicker it can achieve a certain speed.
The simulation result also shows that it would take approximately 6 seconds to achieve 54 kph,
which is 4 seconds less than the given 10 seconds time limit.
0 5 10 150
10
20
30
40
50
60
70
80
90
100
time (s)
kilo
met
ers/
hour
Car Weight 500 kgCar Weight 300 kg
24
Although the simulation was performed for both 300 kg and 500 kg of weights, all the
calculations were done assuming the car would have a weight of 500 kg. However, if an electric
only car is built, the weight needs to be much lower. In 2009 Formula Hybrid competition, there
were two electric only cars. They were from Arizona State University and Tufts University. The
weights of their HIPVs were 430 kg and 370 kg, respectively [22].
25
CHAPTER 3
POWER STAGE CIRCUIT DESIGN
___________________________________
26
3.1 Converter Type
The speed of a permanent DC motor can be controlled either by varying the voltage or the
current that is supplied to the motor armature through a converter. If the source power supply is a
constant DC voltage, choppers are the best converters to produce such variable voltage or
variable current from the constant power source input. The principle of operation of a chopper is
it chops the input voltage through continuous and consecutive switching on and switching off of
power semiconductor switches. The sum of on-switching-duration and off-switching-duration is
the total switching period T. The switching frequency fs is simply the inverse of the switching
period. The duty cycle is defined as the ratio of the on-switching-duration and the switching
period. The variation of the output voltage depends on duty cycle; a duty cycle of 1 means the
switch is on all the time and the motor thus receives the full input voltage whereas a duty cycle
of 0.5 means the switch is on only 50% of its switching period and the motor consequently
receives only 50% of the input voltage. Duty cycle can be changed by either of the following two
methods:
Change the switching frequency and keep the on-switching-duration constant.
Change the on-switching-duration and keep the frequency constant.
For the HIPV, it was decided that a constant frequency voltage mode chopper motor drive would
be designed.
3.2 Converter Topology Selection
Among the many topological variations of chopper, four quadrant full bridge converter topology
was selected as the motor controller topology of the HIPV. The full bridge topology was selected
because it enables the controller to rotate the motor both in reverse and forward direction and
also accommodates both forward and reverse regeneration. The four quadrant full bridge
converter topology and four quadrants of operation are shown in Figure 3.1a and Figure 3.1b,
respectively.
27
Figure 3.1a Full bridge 4-quadrant converter topology. Figure 3.1b Quadrants of operation.
This four quadrant circuit can be operated as two two-quadrant choppers in order to obtain
Quadrant I and Quadrant IV operations as well as Quadrant III and Quadrant II operations.
Quadrant I and IV operation has been termed as mode 1 and Quadrant III and II operation has
been termed as mode 2. Switching sequences of both modes are explained in the following
sections [23].
3.2.1 Mode 1 (Quadrant I and IV) Operation
In this mode, switch Ch4 will be kept on and Ch3 will be kept off permanently. This is to ensure
that node a and node b is always shorted either by an on Ch4 or reverse recovery diode D4.
Switching sequences takes places as per the following steps:
a. At t = 0, Ch1 and Ch4 is turned on
together, and battery voltage +E is applied
to the load. Figure 3.2a Step a operation.
b. At t = τon, Ch1 is turned off but current
keeps flowing in D2-load-Ch4-D2 path
because of energy discharging by the
inductor.
Figure 3.2b Step b operation.
28
c. If brake is pressed during forward motoring,
Ch2 is turned on at t = τon. Turing on Ch2
effectively shorts the load out, which causes
a large current build up in the loop and the
current keeps building until it is high
enough to conduct through D1. This
phenomenon causes current direction
reversal.
Figure 3.2c Step c operation.
d. When Ch2 is turned off at t = τoff, the
current flows though D1-battery-D4-load-
D1 loop.
Figure 3.2d Step d operation.
Steps a and b comprise Quadrant I operation because during these steps, both the output voltage
and load current are positive, which means the power is being supplied from the battery and the
car is motoring forward. Steps c and d comprise Quadrant IV operation because in these steps,
the direction of the load current reverses while the output voltage remains positive, and the
reversal of load current direction form positive to negative means current is now being supplied
to the battery from the load. During Quadrant 1 operation, the circuit works as a buck converter
whereas during Quadrant IV operation, the circuit works as a boost converter. The current and
voltage waveforms of mode 1 operation are given in Figure 3.3.
29
Figure 3.3 Switching sequence (iG1, iG2, iG3, iG4), output voltage (Vld), load current (ild), and
battery current (iB) waveforms during mode 1 operation.
3.2.2 Mode 2 (Quadrant II and III) Operation
Mode 2 operation is very similar to mode 1 operation; in this mode Ch3 is kept on and Ch4 is
kept off permanently. When Ch2 is turned on at t = 0, negative battery voltage –E is applied
through the motor and it causes the motor to run in reverse direction. At t = τon, Ch2 is turned off
but the inductive load keeps the current flowing though Ch3-load-D1-Ch3 loop to discharge
energy. When brake is pressed during reverse motoring, Ch1 is also turned on at t = τon, and it
effectively shorts out the load. The inductive load however continues the current build up in the
short circuited loop until the current is high enough to conduct through D3. At t = τoff, Ch1 is
30
turned off and current flows in the D3-battery-D2-load-D3 loop. This is positive current direction
and is attributed for reverse regeneration.
The current and voltage waveforms of mode 2 operation are given below in Figure 3.4.
Figure 3.4 Switching sequence (iG1, iG2, iG3, iG4), output voltage (Vld), load current (ild), and
battery current (iB) waveforms during mode 2 operation.
The motor controller will include a discrete switch that will allow the driver of the car to choose
either mode a or mode b of operation when the speed of the car is zero.
31
3.3 Semiconductor Switch Realization
Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is a type of transistor that can be
used as a switch in power electronic circuits. Because of having low on-state resistance, high
switching frequency, simple control method and superior safe operating area (SOA) compared to
other semi-conductor devices like Bipolar Junction Transistors (BJT) and Silicon Controlled
Rectifiers (SCR), MOSFETs have become the number one choice of semiconductor switch
implementation in applications that require less than 200 volts, including automotive applications
[24]. For the power converter of HIPV, N-channel MOSFET was the choice of power switches.
Compared to P-channel MOSFETs, N-channel MOSFETs have lower on state resistance and
higher current rating. Also the students doing this project previously built a buck converter using
N-channel MOSFETs and thus had the experience of working with this type of MOSFET.
The selection of the MOSFETs was primarily made based on the maximum blocking voltage and
maximum drain current. The maximum current allowed in the converter is 100 A and the
maximum voltage is 48 V. Based on these constrains, the chosen MOSFET was
IXTH250N075T, manufactured by IXYS Corporation. The salient properties of the chosen
MOSFET in the light of HIPV’s requirements are briefly explained in section 3.3.1.
3.3.1 MOSFET Salient Properties
Maximum Drain to Source Voltage: The maximum drain to source voltage is the voltage the
MOSFET can withstand. At any point of operation the MOSFET is not allowed to see a voltage
that exceeds its maximum blocking voltage. The conservative approach is to choose MOSFET
with voltage rating that is at least 30%-50% higher than the maximum voltage it will have to
block in the circuit. The chosen MOSFET has voltage rating of 75 V, which is about 56% higher
of its maximum blocking voltage of 48 V.
Maximum Continuous Drain Current: This is the maximum current that is allowed to conduct
between source and drain. Commercially available MOSFETs’ current rating is given for
temperature measure of 25oC. However, increase in temperature causes dropping in current
rating. Since high power motor drive applications are often required to operate in harsher
32
surroundings, temperature often goes beyond 25oC; therefore MOSFET with very high current
rating was chosen. The maximum allowable current is 100 A and the current rating of the chosen
MOSFET is 250 A.
MOSFET On-State Resistance: This is the resistance between the source and drain of the
MOSFET. This resistance is dependent on the ambient temperature and the voltage applied
between gate and drain. High temperature increases the on-state resistance. This on-state
resistance is responsible for power losses during current conduction. The chosen MOSFET’s on-
state resistance value is 3.3 mohm.
Maximum Power Dissipation: This property is also dependent on ambient temperature as it is
defined as [25]:
max
max 25
j
oj
D RCT
P
(3.1)
Here DP is the maximum power dissipation, maxjT is the maximum junction temperature and
maxjR is the junction to case thermal impedance. As per Equation 3.1, if the ambient
temperature goes beyond 25oC, the amount of power the MOSFET can dissipate will decline.
Assuming 15 kHz operating frequency, the total power dissipation in a MOSFET during
motoring is shown in Figure 3.5.
Figure 3.5 Semiconductor switching loss during motoring.
33
The total loss that occurs in the MOSFET is the sum of the loss in the MOSFET and the loss in
the freewheeling diodes. As discussed in section 3.2, built-in diodes connected reversely across
the switches freewheel the load current when the MOSFETs are in off-switching state during
motoring and carry the regeneration current during the regeneration. The freewheeling diodes of
the chosen MOSFETs have the same current and voltage rating as that of the MOSFETs.
The losses in the MOSFET devices were calculated using formula given in Equation 3.2.
22
)(
)(
2 sfiOpeakMOSOonDSrmsMOS
srrriDrrOpeakMOSO
offturnconductiononturnOMOSFET
ftVIVRI
fttIVIVPPPVP
(3.2)
The power loss in the freewheeling diodes during motoring, also shown previously in Figure 3.5,
was calculated according to the following formula:
fdDD VIP (3.3)
The highest total loss is approximately 100 W. Keeping in mind that high temperature will
increase power losses while decrease power dissipation ability of MOSFETs, the MOSFETs
were chosen such that its maximum power dissipation ability is considerably higher than the
calculated value. The PD of the chosen MOSFET is 550 W and estimated maximum power loss
at ambient temperature is about 100 W.
For the regeneration mode, the maximum allowed current is 40 A. Thus it can be inferred that
the regeneration loss will be less than the motoring loss.
34
3.3.2 Freewheeling Diodes and Its Salient Properties
From the graphs it is seen that that worst case loss during diode conduction is approximately 100
W, which is considerably below the specified maximum energy dissipation of 500 W. Adding
external diodes with lower forward voltage drop would have improved the power loss and
heating, but the voltage, current and power loss rating of the built in diode adequately meets all
the requirement and thus no external diodes were added across the MOSFETs to save the cost.
3.3.3 Thermal Design
Whether a heat sink is required for the given power electronic design could be found from
Equation 3.4.
lossajaaj PRTT (3.4)
Here ajT is the junction to ambient temperature, aT is the ambient temperature, jaR is
junction to ambient thermal resistance, and lossP is the total loss in the MOSFET.
The thermal resistance for the chosen MOSFET is 0.52 0C/W, the loss is 100 W and assuming 40 0C ambient temperature, the junction to ambient temperature is:
ajT = 40 + 100 x 0.52 = 92 0C.
The chosen MOSFET’s operating range is -25 to 175 0C. This means no heat sink is required.
3.4 Gate Drive Circuit
A gate drive is a power amplifier circuit that accepts a low power input signal and produces
suitable high current gate signal to turn on the MOSFETs.
35
Gate drive is necessary because the PWM signal from the micro-controller cannot provide the
necessary output current and voltage needed to drive the gate capacitance of MOSFETs. For N-
Channel MOSFETs, the voltage at the gate must be 10 V greater than the voltage at the source.
This 10 V difference between the gate and source can be easily created for a MOSFET in a half
bridge that is grounded. However, for the MOSFET that is floating in the half bridge, this 10 V
supply is difficult to provide as the source voltage of the floating MOSFET may not be zero. A
gate drive circuit solves that problem.
An actual MOSFET includes many parasitic elements. These parasitic elements are shown in
Figure 3.6. The parasitic components are gate-to-source capacitance (CGS), gate- to- drain
capacitance (CGD), drain-to-source capacitance (CDS), and internal gate resistance (RG). The
source inductance (LS) and drain inductance (LD) depend on the design of the MOSFET package
[26].
Figure 3.6 Simplified MOSFET Model showing parasitic components [26].
The gate- to- drain capacitance (CGD) is known as the Millar capacitance.
The MOSFETs are intended to be either in fully turned on state or in fully turned off state.
Although desired, MOSFETs cannot be turned on and turned off instantly, and the transition
36
period between the turn on and turn off causes losses. The transition time depends on the time
required to charge and discharge the Miller capacitor, one of the parasitic components. An
important attribute of the gate drive is therefore its ability to quickly pass thorough this Miller
Plateau Region during switching transition. Figure 3.7 shows the gate voltage vs. total gate
charge graph for the chosen MOSFET.
Figure 3.7 Gate voltage vs. total gate charge graph for the chosen MOSFET (taken from
MOSFET datasheet).
The chosen gate drive IC was LM510A, a bootstrap gate driver from National Semiconductor. Its
floating MOSFET driver can operate with supplies up to 100 V. Turn off propagation delay is 25
ns and the IC can drive up to 1000 pF with 15 ns rise and fall time. The gate drive circuit
connection is shown in Figure 3.8.
Figure 3.8 Gate drive circuit.
37
3.5 Pre-Charge Circuit
When a high voltage DC power system is powered up, the step response of the input voltage
causes a high inrush current to flow in the ripple filter capacitor since the capacitor charge is zero
prior to system activation. As the capacitor gets charged and its voltage rises gradually, the
inrush current decreases and it decays exponentially. However, the initial high inrush current,
which may reach up to 1000 A [27], is adequate to stress up the capacitor and damage the
component. This high inrush current may also blow the fuse and damage the switches,
contractors and the battery cells as they are not rated for such high current. The objective of the
pre-charge circuit is to charge the throw capacitor of the system through a controlled current
before connecting the main power stage circuit with the DC supply source. The input current is
limited through a high power resistor. The high inrush current and its exponential decaying are
shown in Figure 3.9a. The pre-charge circuit designed for the TAMUQ HIPV power train is
shown in Figure 3.9b.
Figure 3.9a High inrush current and its exponential decay [28].
Figure 3.9b The pre-charge circuit designed for TAMUQ HIPV power train.
As shown in Figure 3.9b, the pre-charge circuit designed for TAMUQ HIPV power train has two
switches. When the driver will close the switch SW2, the throw capacitor will be charged
38
through the current limiting resistor R17. Through a voltage divider, there will be capacitor
voltage feedback provided to the micro-controller. If the capacitor voltage reaches close to the
battery voltage, the LCD screen will tell the driver that the capacitor has been charged
successfully and the power stage can be enabled. The driver may then proceed and switch on the
switch SW4. It is a double pole single throw (DPST) switch. It shorts out the current limiting
resistor and connects the power stage with the battery supply simultaneously.
The pre-charge circuit provides protection to the ripple capacitor, the battery and the fuse. This
circuit will also work as part of power train’s fault detection system. The micro-controller will
allow 10 seconds for the filter capacitor to charge up. If the capacitor fails to charge within 10
seconds (if the capacitor is not faulty, the charging should take less than 2 seconds) from start up,
the LCD will tell that driver that there is fault in the capacitor and the system will shutdown.
39
CHAPTER 4
CONTROL CIRCUIT DESIGN
_____________________________________
40
4.1 Microcontroller Interfacing with Accelerator and Brake
To input the amount of throttle desired by the driver, a Bosch accelerator, which had an
acceleration pedal position sensor (APPS) attached with it was used. The accelerator was bought
by Dr. Shehab from Egypt. It was a second hand component and thus there came no datasheet
along with this piece of equipment. The Bosch accelerator is pictured in Figure 4.1.
Figure 4.1 The acceleration pedal.
It was however known that APPS was a linear variable resistor as it indicated the position of the
accelerator pedal in the form of variable resistance. The APPS had six pins in total. Using the
Agilent multi-meter, the variable resistance range between any two pins of different
combinations was measured. It was found that different pin pairs produce different range of
variable resistance. The greatest range was 2.346 kΩ - 1.732 kΩ and it was found between pin 2
and pin 4, with the pin number counted from the top of the APPS.
The ADC of the micro-controller required all analogue inputs to be voltage signals in the range
of 0-5 V. Thus for the APPS to be interfaced with the micro-controller, it needed some support
circuitry to produce a linear voltage of 0-5 V, with 0 volt specifying the pedal at idle position and
5 V specifying the pedal at wide open throttle (WOT) position. As shown in Figure 4.2, the
support circuitry included a Wheatstone Bridge, an amplifier and a differential amplifier.
41
Figure 4.2 Interfacing the MCU with the APPS.
Both resistors R1 and R2 were 10 kΩ. R3 was 3 kΩ. When pedal was at idle the resistance was
2.346 kΩ, which means the leg of Wheatstone Bridge to which APPS was connected needed an
excess of 654 Ω of resistance to achieve the null. This excess resistance was provided by a 5 kΩ
potentiometer. After the null was achieved, the floating voltage between node A and node B of
the Wheatstone Bridge was measured with the pedal at idle and at WOT. This floating voltage
range was found to be 1.136 V-2.27 V. An op-amp with a gain of 4.4 then amplified this voltage
range up to approximately 5 V-10 V. Finally a differential amplifier was used to subtract 5 V
from this range and get accelerator input voltage range level-shifted to the required range of 0-5
V. This interfacing circuit was built on the breadboard and tested.
As for the brake, a pedal similar to acceleration pedal was needed. Due to time constraint,
however, ordering another pedal and getting it before the demo day was not possible. Therefore
it was decided to use a 5 kΩ potentiometer instead. Generating the desired analogue signal from
the pot was straightforward and simple. The first terminal of the potentiometer was connected
with the 5 V power supply and the third terminal was grounded. The second terminal, the slider,
was connected with micro-controller. The voltage at the slider terminal with respect to the
ground varied from 0-5 V as the pot resistance was increased from 0 to 100%. The brake circuit
is shown in Figure 4.3.
42
Figure 4.3 The brake circuit. The right shows the brake at idle position while the left shows the
brake at WOT position.
4.2 Current Limiting Circuit
Among the four feedback signals that go into the micro-controller, the most important was the
motor current feedback. A current limiting circuit measures the steady state current that is
flowing into the motor and sends the reading to the micro-controller to be compared with the
programmed value of maximum allowable current for a particular mode of operation. If the
current exceeds the desired maximum value, micro-controller changes the PWM signal duty ratio
accordingly to lower the armature voltage and bring the motor current under the set limit. Fast
and accurate current sensing is critical for two reasons: (i) to prevent the MOSFET bridges from
being damaged by over current (ii) to prevent demagnetizing of the motor by keeping the
armature reaction effect in check.
There are several ways of sensing the current. The classical approach is to add a shunt resistor in
series with the current path and measure the voltage across it. The problem with this approach is
it does not offer any voltage isolation and thus should not be used for high current sensing.
For this design, Hall Effect current sensing was employed. If a current carrying plate is placed in
a magnetic field that is perpendicular to the motion of the charge carriers, namely electrons and
holes, a force called Lorentz Force acts upon them. The Lorentz force makes the charge carriers
deviate from their original straight line conduction path. The direction of the deviation is
43
determined as per Fleming’s Left Hand Rule. Since the electrons and the holes have opposite
charges, they move away from each other and get accumulated on the opposite edges of the
conducting plate. This gives rise to a voltage across the plate, which is known as the Hall
Voltage. The whole Hall Effect process is illustrated in Figure 4.4.
Figure 4.4 Hall Effect [29].
The mathematical expression of the hall voltage is given in Equation 4.1.
dneIBVH
(4.1)
Here VH is the hall voltage, I is the current, B is magnetic flux density, d is the thickness of the
conductor, e is the electron charge and n is the charge density.
The chosen current sensor was ACS756; a current sensor manufactured by Allegro Microsystems
Inc. The sensor’s internal structure is shown in Figure 4.5a . The current to be measured is
passed through a shunt path that has resistance value in the order of few milliohms. The low
resistance minimizes the conduction loss and it therefore works well for automotive applications
where high current sensing is required. The Hall-effect sensor, which sits close to the shunt path,
produces a hall output voltage that is proportional to the strength of the magnetic field created by
current flowing through the shunt. This can also be understood from Equation 4.1. According to
44
amperes law, more current means stronger magnetic field, and stronger magnetic field means
more hall voltage. A ferrite core wraps the shunt path as it helps the magnetic flux generated by
current carrying wire to concentrate around the sensor [30].
This sensor IC does not require any other external support circuit. The sensor connection
diagram is shown in Figure 4.5b.
Figure 4.5a Hall sensing method [30] Figure 4.5b Chosen Hall sensor connection diagram.
Allegro ACS756 Hall Effect sensor provides a voltage isolation of 3 kVRMS. This IC is also
very cheap, needs a 5 V power supply and senses current in both direction (motoring and
regenration current). This current sensor provides a 2.5 V output for zero current, 4.5 V for
maximum postivie current current (maximum positive current is 100A) and 0 V for maximum
negative current (maximum negative current is -40 A).
4.3 Speed Limiting Circuit
The speed limiting circuit was required for two reasons (i) to limit the speed of the motor, and
(ii) to measure the speed and display it in the speedometer. The speed limiting circuit measures
45
the speed of the motor and feedbacks it to the micro-controller to be compared with reference
value (provided by driver) and the programmed value of maximum allowable speed for a
particular mode of operation. If the speed limit is below the value desired by the driver or above
the maximum set limit, the micro-controller changes the PWM signal duty ratio accordingly to
increase or decrease the armature voltage as necessary.
The speed limiting circuit for the TAMUQ HIPV consisted of two components: a tachometer and
a frequency to voltage converter IC. As for the tachometer, an optical rotary encoder was chosen
from US Digital. It was an incremental type encoder. The encoder contains a light source, a
photo detector, a disk which has uniformly spaced opaque and translucent stripes on it, and a
small PCB that contains some logic circuitry. The disk is mounted on the motor shaft, the light
source emits light on the disk from one side and the photo detector from the other side detects the
light pulses that pass through the translucent stripes. This arrangement provides a digital means
of measuring the angular displacement of the motor shaft. How many light pulses are generated
for a single rotation of the motor shaft depends on the number of translucent stripes the disk has.
In our case, the disk had 32 translucent stripes, which means the encoder generated 32 pulses for
each rotation. The pulses are counted up by the digital logic circuitry and it generates the output
in the form of a square wave signal. The chosen encoder is shown in Figure 4.6.
Figure 4.6 The chosen incremental encoder.
The digital output could have been easily fed to the micro-controller without using a frequency
to voltage converter as the micro-controller is capable of determining the speed by measuring the
46
frequency of the square wave signals. This procedure would have produced more accurate speed
measurement too. However, counting such high frequency pulses could have required the micro-
controller to spend a considerable amount of time in speed measurement, which it could not
afford as it had to oversee some other more important control tasks like current limiting
simultaneously [31].
As a solution, a frequency to voltage converter IC LM2917 was used. This was an easy IC to use
and through some careful combination of resistor and capacitor values, the IC could produce
desired 5 V analog signal for the maximum allowable speed of the motor (2500 RPM). The
desired resistor value and capacitor value are determined from Equation 4.2.
Vout = fin x VCC x R28 x C11 (4.2)
The TAMUQ HIPV motor will have the maximum speed of 2500 RPM and the chosen encoder
has 32 counts per revolution. It equates to a square wave signal of 1.3 kHz. The desired output
voltage for the maximum speed was 5 V. By trial and error, R28 and C11 were chosen to be 310
kΩ and 0.001 uF, respectively.
fin = (RPM) x (32 / 60) = 2500 x (32 / 60) = 1333.33 Hz
VCC = 12 V
R28 = 310 kΩ
C11 = 0.001 uF
Vout = 1333.33 x 12 x 310k x 0.001u = 5 V
The speed limiting circuitry is shown in Figure 4.7.
47
Figure 4.7 Speed limiting circuit-encoder and frequency to voltage converter.
4.4 Battery Voltage and Power Stage Voltage Feedback
Providing the voltage feedback and power stage voltage feedback to the micro-controller were
also important as these feedbacks were part of protection and fault detection systems. Depending
on the battery voltage feedback, the micro-controller decides if the voltage is too high or too low.
If the battery voltage is above 48 V or below 24 V, the system will automatically shutdown to
protect the system from overvoltage and undervoltage, respectively. The battery voltage
feedback also is required to determine whether the current should be regenerated if the brake is
pressed. If regeneration occurs when the battery is close to its nominal voltage, it may cause
overvoltage, which in turn will cause the system to shutdown. This is an unwanted occurrence as
braking is not intended to shut down the system. That is why regeneration will be allowed only
when the battery voltage is below 75% of its nominal voltage.
As previously described, micro-controller needs the ripple capacitor voltage feedback to
determine if the capacitor has been properly charged before switching on the power stage or to
determine if the capacitor has a fault based on the time it takes to charge it up and achieve a
voltage close to battery voltage.
48
The voltage feedbacks were provided by voltage divider circuits. A combination of 500 Ω and
4.3 kΩ resistors can produce a voltage feedback of 5 V when the battery or capacitor voltage is
48 V and a feedback of 0 V when the battery or capacitor voltage is 0 V.
5485003.4
500
k; 00
5003.4500
k
The voltage divider circuits are shown in Figure 4.8.
Figure 4.8 Power stage and battery voltage feedback.
4.5 Power Supply for Gate Drive and other ICs [32]
Both the low power control circuit and the power stage circuit have to be powered from the
vehicle on board battery pack. Compared to the power stage circuit, the power consumption of
the control circuit is fairly low as most of the control circuit components require 12 V or 5 V
power supply.
To provide the 12 V power supply, a built in switch mode buck converter IC LM2576 was
chosen from National Semiconductor. Switch mode power supply IC was preferred over linear
power regulator because the power dissipation is lower in a switch mode buck converter
compared to a linear regulator.
49
For 5 V power supply, a linear regulator LM7805 was used. As the current drawn by the ICs that
require 5 V power supply is very low, the power dissipation will be negligible.
The schematic of the entire power supply circuitry is given in Figure 4.9.
Figure 4.9 Power supply circuitry.
4.6 Shoot-Through Protection Logic [33]
Whether the power train system is regenerating or motoring, at any instant only two MOSFETs-
one from the left side half bridge and one from the right side half bridge should be on. The left
side and right side MOSFET half bridges are illustrated in Figure 4.10.
Figure 4.10 Left side and right side MOSFET half bridges.
50
Shoot though is a short circuit condition that occurs when both MOSFETs of a half bridge are
simultaneously tuned on. The shoot-through condition may destroy the MOSFETs.
To prevent the occurrence of shoot-though, a protection circuitry was employed using AND and
NAND gates. The protection circuit shown in Figure 4.11 is for the left side MOSFET half
bridge.
Figure 4.11 Shoot-through protection logic scheme.
The protection procedure could be summarized as follows:
Both HI and LO are 1 →NAND produces 0 → AND1 nulls the PWM → No shoot-
though.
Both HI and LO are 0 → AND2 and AND3 ensures no gate signal irrespective of PWM
HI ≠ LO, Gate signals are provided accordingly.
A similar protection logic circuitry was built for the right side MOSFET bridge.
4.7 Electro-Magnetic Compatibility (EMC) Considerations
Any motor controller is susceptible to electrical noise and electro-magnetic interferences (EMI).
EMIs and electrical noises are generated from various sources. The semiconductor devices
constantly switch on and off large amount of current at high voltages [34], which generates
unwanted signals of higher frequency known as EMIs. In a digital motor control circuit, the
51
crystal used for the micro-controller is another source of EMI. Other sources of EMIs are high
voltage DC power supply, atmospheric noise and vibration generated by a rotating electric
motor, inrush current and rapid collapse of current in inductive elements. These electrical noises
and EMIs are transmitted though radiations in space or conduction along cables and PCB traces
and affect the proper functioning of some components of the control circuit. Gate drive circuits,
current sensors, and micro-controller for example are very sensitive to EMIs.
If a motor controller system is designed such that the controller does not generate EMIs above a
level set by a particular standard, then the motor controller is said to have electromagnetic
compatibility (EMC) as per that standard. Commercial motor controllers adhere to either local
standard or IEEE standard. The local standard in the United States is Federal Communication
Standard (FCC). In UK and Germany, the local standards are British Standards Institution (BSI)
standard and Verband Deutscher Elektroingenieure (VDE) standard, respectively. Most of these
standards are the local equivalent of IEEE standards [35].
As previously mentioned, it was not possible to manufacture a motor controller in our lab that
would fully adhere to a particular standard and has complete immunity from EMIs. It is because
extensive testing is required to determine the actual level of EMI and electrical noise and the
procedure is expensive and time consuming. Nonetheless, some EMI protection schemes have
been included and they are discussed in sections 4.7.1 and 4.7.2.
4.7.1 Snubber Circuit
Although the MOSFETs chosen for the motor drive has voltage rating that is 54% higher than
the voltage it will have to see through, high voltage spikes is always a possibility in motor drive
applications due to high switching frequency and high inductive load. A snubber circuit protects
MOSFETs from such high voltage spikes. Other reasons for adding snubbers across the
MOSFETs are:
Reduce EMIs.
Carries power dissipation from the semiconductor switch to the snubber.
52
The RC snubber was designed following a snubber design procedure outlined by Dr. McMurray
in one of his papers [36]. The snubber resistor and capacitor value determination formulae are:
0
2
0
0
p
S
LEIC (4.3)
S
PS C
LR 02 (4.4)
Here
0I = maximum current, 100 A.
0E = maximum blocking voltage 48 V.
0 = initial current factor. This current factor was determined from the graph shown in Figure
4.12a. To find the current factor, first the ratio of an arbitrarily chosen maximum voltage (100 V)
and maximum blocking voltage is found. That ratio was 2.1 (100/48) volt. From the graph, the
current factor corresponding to ratio 2.1 is 1.9.
0 = damping factor. The damping factor that corresponds to initial current factor value of 1.9 is
0.5.
PL = characteristic impedance of the PCB circuit, estimated to be 43 nH.
Plugging these values in Equation 4.3, the snubber capacitance was found to be 100 nF. From
Equation 4.4, the snubber resistance was found to be 0.68 ohm.
Figure 4.12b shows the snubber circuit connected across the MOSFET.
53
Figure 4.12a Initial current and damping factor [37]. Figure 4.12b Snubber circuit.
4.7.2 Filters for Feedback Voltage Signals
The RC filter circuit is shown in Figure 4.13.
Figure 4.13 RC filter circuits for feedbacks.
54
The corner frequency was chosen to be about one tenth of the PWM frequency [38]. If for any
reasons the voltage feedback signal becomes greater than 5 V, voltage clamps protect the micro-
controller.
55
CHAPTER 5
MICRO-CONTROLLER MODULE,
FIRMWARE DEVELOPMENT & FIRMWARE
SIMULATION
_____________________________
56
5.1 Digital vs. Analog Control
There are two ways a motor drive control could be designed: analogue control and digital
control. Both types of control have its own costs and benefits. Although the design process is
complex and expensive, analog motor control is less vulnerable to electrical noise and is
therefore more reliable even in harsh operating conditions. Also making corrections in the
analogue control circuit after it has been designed is an enormously challenging, tedious and
time consuming process. Digital motor control on the other hand is cheap, faster, and making
corrections and changes during the testing of the control circuit is easier as the program loaded
into the digital device (micro-controller or FPGA) can be reprogrammed quickly. However,
digital motor drives are susceptible to electrical noise and magnetic interferences and thus
require extra noise protection measure.
Considering the cost and the easiness of the design procedure, it was decided that a micro-
controller based digital motor drive would be used for the TAMUQ HIPV drive train.
5.2 About the Chosen Microcontroller Module
The micro-controller chosen for HIPV’s motor drive design was PIC16F877A, a well known
product of Microchip Technology Inc. This micro-controller was an ideal solution because it was
inexpensive, available in most power electronics component distributors, and it provided with all
the features that were required in designing this motor drive. The device has an operating
frequency of 20 MHz, requires a power supply of 5 V, and has automatic power saving mode.
The device is based on reduced instruction set computer (RISC) architecture, which makes the
execution faster. This micro-controller takes only one cycle to execute the program instructions
except for the branch instructions, which take two cycles to execute. The micro-controller has
8k of ROM FLASH memory, and this FLASH technology allows the firmware (the
programming code written for the micro-controller) to be burned into and erased from the micro-
controller as many as 100,000 times. Some other features of the microcontroller are described in
detail in the following sections.
57
5.2.1 Analog to Digital Converter (ADC)
All the inputs to the microcontroller- the accelerator pedal position, the brake pedal position,
power stage voltage, battery voltage, motor current feedback and motor speed feedback were
analogue voltage signals. Since the micro-controller is a digital device, it needed an analog to
digital converter module to measure and read all these input signals. The chosen micro-controller
includes a built in ADC module and eight ADC input channels.
The ADC module of the PIC16F877A uses a method called successive approximation
conversion to produce a digital value of an analog input. In successive approximation
conversion method, the input value is first compared with the half of the input range. If the input
value is over or under the half range, the input value is then further compared with three quarter
or one quarter of the input range, respectively. The resolution of the conversion depends on the
number of comparison steps [39]. After the conversion, the PIC16F877A micro-controller stores
the result in ADRESH and ADRESL registers.
Through successive approximation conversion, the PIC16F877A micro-controller produces a 10-
bit binary result for a particular voltage input. As shown in Figure 5.1, the minimum 0 V
corresponds to 0x0 and maximum 5 V corresponds to 0x03FF.
Figure 5.1 Analog to digital conversion [40].
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This 10 bit resolution result gives a precision of × 100% = 0.1%, which was more than
enough for the given design.
Among the eight available A-D channels of the micro-controller, two channels were used to
provide with external voltage references through which maximum and minimum analog input
voltage limits were set. The maximum analog input was set to 5 V and the minimum analog
input was set to 0 V. Providing external voltage references improve the A-D conversion
accuracy.
In A-D conversion, the data acquisition time and conversion time are very important. The
acquisition time is the time required by the holding capacitor to charge itself up to input voltage
level. This acquisition time depends on the input impedance and the ambient temperature. The
worst possible acquisition time could be 20 µs. The exact acquisition time can be calculated
using the formula given in the micro-controller manual. Since the acquisition time is much
greater than the conversion time, care was taken while writing the code to allow adequate time to
charge the holding capacitor before taking a measurement.
5.2.2 PWM
The chosen micro-controller had a built in PWM module which could generate two PWM signals
simultaneously. Two PWM signals are necessary to drive two MOSFETs concurrently, one from
each half bridge.
The PWM signals of the PIC16F877A micro-controller have 8-bit resolution, which means they
can have a variance of 124 steps. Therefore, to vary the duty ratio of the PWM signals as per the
brake and acceleration input, the analog readings (0-1023) had to be divided by four before using
them as the argument of PWM function (0-255).
5.3 Program Algorithm
The program for the power train control circuit was developed using a big loop and two sub-
routines. The loop runs infinitely and calls the shut down and direction check sub-routine when
59
necessary. No interrupt was used. The program algorithm of the direction check sub-routine, the
shutdown sub-routine, and the main loop are given in Figure 5.2a, Figure 5.2b and Figure 5.3,
respectively.
Figure 5.2a Direction check sub-routine. Figure 5.2b System shutdown sub-routine.
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Figure 5.3 The big loop.
Most of the algorithm is easy to understand and is self-explanatory. After the system is powered
up, a welcome message is shown. The micro-controller then initializes the PWM, sets data
direction registers and configures ADC. The system then charges the filter capacitor. If there is
no fault with the pre-charge, it asks the driver to enable the power stage.
After power stage is enabled, the direction is checked. Then depending on the brake and
accelerator reading, system operating mode is determined. The brake overrides the accelerator.
In each mode, the voltage, the current and the speed are checked to see if required MOSFETS be
turned on and if speed and motoring or regeneration current can be increased as per acceleration
or brake input. If any parameter is greater or smaller than the set limit, power stage signals are
immediately disabled and the loop starts again.
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5.4 Firmware Development
After the program algorithm was defined, the firmware development was easy. The firmware
code was written using BASIC language. A software package called Microbasic was used to
write the source code and compile the code into executable hex file. The demo version of the
program can be downloaded for free from Microelektronika website. The demo program offers
full functionality but limits the size of the compiled program to 2 kilo bytes. The source code
development involved numerous stages of re-writing and debugging.
A fully commented firmware code is given in Appendix 3. Anyone following the firmware codes
along with the comments and the program algorithm should be able to decode it easily.
Before writing the code for the big loop and program the sub-routines, the special function
registers (SRF) had to be configured correctly. The configuration of the SRFs that were used in
the firmware of the power train system is described below in detail.
5.4.1 TRIS Register
The input-output pins of PIC16F877A micro-controller are classified into five groups: Port A, B,
C, D and E. By setting the respective TRIS register, a group of ports could be configured as input
or output ports. Like TRISA=1 sets all the port A pins as input and TRISA=0 sets all the port A
pins as output. In the power train system firmware, Port A, B and E are configured as input and
Port C and D are configured as output.
5.4.2 ADCON1 Register
The ADCON1 control register bit configuration is given in Table 5.1.
Table 5.1 ADCON1 register configuration bits.
Bit Explanation
Bit 7 1
A-D converter produces a 10 bit binary number any voltage input. However, any micro-controller register can hold only 8 bits. Therefore two registers, ASRESL and ADRESH are
62
used to save those 10 bits. Configuring bit 7 as ‘1’ means Conversion result is right justified. Six most significant bits of the ADRESH remains unused.
Bit 6 0 unimplemented bit, read as 0 Bit 5 0 0 indicates the that Vss (0V) is the minimum analog input. Bit 4 0 1 indicates the that Vdd (5V) is the minimum analog input. Bit 3 0 unimplemented bit, read as 0 Bit 2 0 unimplemented bit, read as 0 Bit 1 0 unimplemented bit, read as 0 Bit 0 0 unimplemented bit, read as 0
5.4.3 OSCCON Register
The OSCCON register configuration bits depend on the type of clock used for the system. There
could be four types of clock: low power low frequency quartz crystal (LP), intermediate-
frequency quartz crystal (XT), high frequency crystal (HS) and resistor-capacitor oscillator (RC).
Since the clock was provided from a 20 kHz quartz crystal, HS was chosen as clock from the
Edit Project Settings (Shown in Figure) and Mikrobasic then automatically configured the
OSCCON register bits.
5.4.4 Watchdog Timer [41]
Watch dog timer automatically resets the micro-controller after a given time period. Watch dog
timer is enabled in programs where it is feared that a run-time condition might cause the program
to enter into unwanted endless loop. For the power train program, watch dog timer was disabled.
5.4.5 Power Up Timer [42]
This timer “provides a nominal 72 ms delay between the power supply voltage reaching the
operating value and the start of program execution”. As a precaution, the power up timer was
enabled to ensure that supply voltage is stable before the start of the clock.
5.4.6 Brown Out Reset [43]
If brown out reset is enabled, it holds the micro-controller program execution in reset at the
occurrence of a momentary supply voltage drop, known as brown out. Brown out was on for the
power train source code.
63
5.4.7 Low-Voltage Programming Mode [44]
The low voltage programming mode is selected to allow the whole programming to be done for 5
V power supply. Low voltage programming was disabled for the power train program.
5.4.8 Electrically Erasable Programmable Read Only (EEPROM) Memory [45]
EEPROM memory was not used. So EEPROM protection enabling or disabling made no
difference.
The configuration bit settings are shown in Figure 5.4.
Figure 5.4 Configuration Bits.
5.4.9 Pin connections
The full listing of the assigned functions of all the pins of the micro-controller is given in Table
5.2.
Table 5.2 Micro-controller pin assignment.
Port No Port Name Direction Function
1 Vpp x Reset 2 RA0 Analog Input Accleration
64
3 RA1 Analog Input Brake 4 RA2 Analog Input Current Feedback 5 RA3 Analog Input Voltage Reference 6 RA4 x x 7 RA5 Analog Input Battery Voltage 8 RE0 Analog Input Speed Feedback 9 RE1 Analog Input Power Stage Voltage Feedback
10 RE2 x x 11 Vdd x 5V 12 Vss x GND 13 OSC1 x CLK 14 OSC2 x CLK 15 RC0 x x 16 RC1 Digital Output PWM2 17 RC2 Digital Output PWM1 18 RC3 Digital Output HI/Q1 19 RD0 x x 20 RD1 x x 21 RD2 Digital Output LCD D7 22 RD3 Digital Output LCD D6 23 RC4 Digital Output L/Q2 24 RC5 Digital Output R/Q4 25 RC6 Digital Output F/Q3 26 RC7 x x 27 RD4 Digital Output LCD D5 28 RD5 Digital Output LCD Enable 29 RD6 Digital Output LCD D4 30 RD7 Digital Output LCD RS 31 Vss x GND 32 Vdd x 5V 33 RB0 34 RB1 Digital Input Power Stage Enable 35 RB2 Digital Input F/R switch 36 RB3 x x 37 RB4 x x 38 RB5 x x 39 RB6 x x 40 RB7 x x
65
5.4.10 Scaling Factors The maximum and minimum values of the drive parameters are in volts, amperes and rpm. Since
the micro-controller does not understand these values, the maximum and minimum parameters
had to be set in terms of their equivalent ADC reading. The equivalent ADC reading was
obtained by multiplying parameter values with scaling factors. The scaling factors of all the
parameters are tabulated in Table 5.3.
Table 5.3 Drive parameters and Scaling Factors.
Parameter Scaling Factor Storage Format Voltage Feedback 1023/48 = 21.3 1023 = Max 48 V, 0 = Min 0 V
Speed 1023/2500 = 0.4092 1023 = Max forward speed (2500 RPM) 511 = Max reverse Speed (1250 RPM)
Current 1023/100 =10.23
1023 = Max forward current (100 A) 511 = Zero current 0 = Maximum reverse current (-40A)
5.5 Simulation of Firmware
The whole firmware was simulated using a software called Proteus Virtual System Modeling
(VSM) of Labcenter Electronics. Fortunately this software had a virtual PIC16F877A model
where the hex file could be downloaded and the whole system could be simulated for the written
source code.
The circuit used for the simulation is given Figure 5.5. This circuit is slightly different from the
actual power train circuit given in Appendix 4. For example, instead of building the whole power
stage circuit and current limiting circuit for the current feedback, a simple potentiometer was
used instead. Because it was known that the current feedback would be within the range of 0-5
V, and this feedback voltage range could be achieved by a potentiometer. The reasons why
actual circuit could not be used for simulation are:
66
Some circuit components were not available in the Proteus VSM library. For example, to
measure the regeneration and motoring current, a bidirectional sensor was needed.
However, only unidirectional hall sensors were available in the VSM library.
Even this simple circuit loaded the CPU 95% during simulation and the VSM also could
not produce real time simulation. Simulating the actual circuit, which is much more
complex than the circuit used for simulation only, was therefore out of equation.
Figure 5.5 The circuit used to simulate the firmware in Proteus VSM.
Table 5.4 explains the whole simulation step by step. After the system is activated, it will show a
welcome message.
67
Table 5.4 Step by step explanation of firmware simulation.
Feedback/Input Explanation Output
Driver activates the system, welcome message
is shown.
System performs some self test. It gives 10s to
pre-charge the filter capacitor. If the filter capacitor fails to pre-
charge, the fault message is shown. Then the system
shutdowns.
If the capacitor is successfully charged, LCD
shows “Cap Charged”.
F/R switch is open. LCD therefore shows that the
car is ready to go forward. It also tells the driver to enable the power stage.
Driver now enables the power stage. LCD shows,
“PS Enabled”.
68
The big loop first checks the battery voltage. If it is low, it shows in the LCD
and the system shuts down to prevent it from
undervoltage.
If the battery voltage is OK, the LCD shows the car in forward motoring
mode.
The accelerator pedal is close to WOT, the brake
reads zero, and as expected MOSFET Q1
and Q4 is enabled.
Now while going forward, the direction has been
changed. Soon after the direction is changed, the
power stage is off, and the motor starts spinning
down.
When the motor speed
feedback reads zero, only
69
then the direction is changed.
The car is going reverse, full throttle, brake reads
zero. As expected, MOSFET Q2 and Q3 are
on.
Now brake is pressed. Brake overrides
accelerator. Regeneration was expected, but no
regeneration is happening because the battery
feedback says the battery is full.
70
CHAPTER 6
BATTERY SIZING
_____________________________
71
6.1 Importance of Battery in Electric Vehicles
Batteries are the fuel of the electric vehicles. There are two types of batteries: non-chargeable
and re-chargeable. Electric vehicles use the latter one. This section contains our very
preliminary literature survey about the process of selecting and sizing the appropriate battery
pack for the TAMUQ HIPV. The process includes assessing the needs, comparing the battery
parameters of existing commercial batteries that can fulfill the needs, comparing the costs and
battery parameters of some available commercial batteries, and finally selecting the appropriate
battery type and size.
6.2 Important Battery Parameters [46]
Below are some of the most important battery parameters that must be well understood before
sizing and selecting battery pack for an electric vehicle.
6.2.1 Cell Voltage
All electric cells supply a nominal terminal voltage when current is drawn out of them. An
approximate representation of an electric cell is given in Figure 6.1.
Figure 6.1 Approximate representation of a traction battery cell.
In Figure 6.1, R is the internal resistance of the battery cell whereas E is the electromotive
potential. By Ohm’s law, the terminal output voltage V can be expressed as:
IREV (6.1)
72
Output voltage supplied by the battery is not constant. From Equation 6.1, the output voltage is
equal to the electromotive potential only when there is no supply current. When there is current
flowing out of the battery, the output voltage drops and when current is fed into the battery,
output voltage steadily reaches back to open circuit output voltage or electromotive potential. A
traction battery cell usually has nominal output voltage of 6V or 12V.
6.2.2 Charge Capacity
The amount of charge a battery can contain is quantified by the charge capacity of the battery.
The unit of this quantity is Amp-hours. Charge capacity is affected by many factors like weight,
ambient temperature, age of the battery, and discharge rate, among which discharge rate is the
most important. If the current draining out of the battery is higher than the rated drain current,
the battery may discharge faster than the rated discharge time. The vice versa is also true.
6.2.3 Energy
The energy stored in a battery cell is the product of its terminal voltage and the current it
supplies. Battery energy is measured in Kilo-Watt-Hours.
CVWhE )( (6.2)
Here C is the charge capacity in Amp-hours. Since the charge capacity varies depending on the
discharge rate and the terminal voltage drops as charge is drained from the battery, battery
energy E is therefore a variable quantity.
6.2.4 Specific Energy
Specific energy is the amount of energy stored in per kilogram of battery mass. Its unit is Wh/kg.
Multiplying this quantity with required amount of energy for a system gives a preliminary
estimation about the battery weight.
73
6.2.5 Energy Density
Energy density is the amount of energy stored in per meter cubed of battery volume. Its unit is
Wh/m3. Multiplying this quantity with required amount of energy for a system gives a
preliminary estimation about the battery volume.
6.2.6 Specific Power
Specific power is the amount of power obtained per KG of battery. Its unit is W/kg. How the
specific power of a battery with respect to specific energy changes for a battery is very
important. High specific energy and low specific power means a battery can store a lot of energy
but give it out very slowly over a long range of time. On the other hand, low specific energy
results in high specific power quick drain out energy reduces the energy storage capability of a
battery.
6.2.7 Efficiency
Like any other systems, batteries are not perfect and thus cannot return the entire charge put into
the battery. Like some other factors already discussed, battery efficiency also depends how the
battery is used. Efficiency is expressed as:
edischbeforestatethetoinbatterytheputtorequiredenergyElectricalbatterythebyoutgivenenergyElectrical
battery arg (6.3)
6.2.8 Depth of Discharge
Depth of discharge (DOD) indicates the state of charge in a battery. An 80% DOD means 80% of
the charge has been drained out of the battery.
6.2.9 Other parameters
I. Self discharge rate: Because of the internal resistance, the battery discharges
spontaneously if not used. How fast this discharge takes place should be taken into
account when buying a battery.
74
II. Battery geometry: Battery geometry comes into consideration when battery packs are
designed for electric vehicles.
III. Battery life and number of deep cycle: The number deep cycles that a rechargeable
battery can undergo indicates the life of the battery.
IV. Temperature: Most batteries discharge at a higher rate at temperature higher than ambient
(25 degree Celsius) while battery performance drops of at lower than ambient
temperature. Therefore, when installing battery pack in the electric vehicle, the heating or
cooling needs should be considered and appropriate facility should be installed to keep
the battery run at temperature where it is most effective.
6.3 Need Analysis of TAMUQ HIPV Battery Pack
The primary requirement of the battery pack is its energy capacity will have to be greater than or
at least equal the amount of total energy spent a certain cruising period. It can be expressed as
follows:
tPE peakmotorratedmotorbatt (6.4)
Here battE is the energy capacity of the battery, ratedmotorP is the rated motor power, peakmotor is
the peak motor efficiency and t is the cruise time. The rated power if two of the chosen motor are
used is 12.56 kW and the peak efficiency is 90%. Assuming the maximum time TAMUQ HIPV
will be required to cruise is half an hour (in the endurance test); then according to Equation 6.4,
chosen battery pack then must have energy capacity of 5.652 kWh.
Including the energy capacity requirement, all the requirements of the TAMUQ HIP Car is listed
in Table 6.1.
Table 6.1 TAMUQ HIP Vehicle battery pack needs/constraints specifications.
Need/Constraint Specification Comment
Nominal Voltage 72 V Rated current of the motor
Discharge Rate 200 A Rated voltage of the motor
Minimum Energy 5.652 kWh Equation 3.4
75
Capacity
Maximum Charging Time Less than 10 hours Chosen arbitrarily
Cost Low
Reliability More than 800 cycles
Weight Should be less than 50 KG Chassis simulated for 50 kg battery
pack
Table 6.2 compares different parameters of three commercially available batteries.
Table 6.2 Comparison between Thundersky, Optima Red-Top and Valence batteries.
Manufacturer Thumdersky Optima Red-Top Valence
Type LiIon - LiIon
Part No TS-LFP90AHA 8025-160 RT battery module
Nominal Voltage 4.5 12 12
Capacity (Ah) 90 44 110
Capacity (Wh) 405 528 1320
Weight/Cell (kg) 3.2 14.4 15.8
Cycles at 80% DOD > 3000 >2000 >2500
Volume/Cell (mm3) 215x218x61 237.24x170.18x195.20 260x172x225
No of cells required 16 6 6
Pack Voltage 72 72 72
Pack Energy Capacity 6.48 3.168 7.92
Pack Weight 51.2 86.4 94.8
From the above comparison, it can be concluded that only the Thunder Sky batteries have less
weight and more energy capacity. A Thundersky pack consisting of 16 cells are therefore best
suited to meet the requirements.
76
6.4 Chemistry of the Chosen Battery [47]
In lithium–ion battery, a lithiated transition metal intercalation oxide is used for positive
electrode and lithiated carbon is used for the negative electrode. Either a solid polymer or a
liquid organic substance is used as the electrolyte. Electrical energy is generated from the
reaction where Lithium carbon reacts with a metal oxide to produce carbon and lithium metal
oxide.
77
CHAPTER 7
CONCLUSION
_____________________________
78
7.1 Project Achievements and Incompleteness
At start of the Spring 2010 semester, the project objective was defined as “design, simulate, build
and test a prototype power train”. However, over the course of the semester it was found that
merely the design and simulation of the power train were much more time consuming than
expected at the beginning of the semester. It is because the students working in this project-
never worked with micro-controller before. They had to self-study the architecture of the
micro-controller and understand it.
did not have good knowledge of programming. They therefore had to learn the
programming language themselves and program the micro-controller.
Despite taking lion’s share of the time available, the students at the end were able to complete
the design and simulation 100% successfully. As for the product prototyping and testing, the
students had some sporadic successes. These sporadic successes are illustrated in the photos
below:
Figure 7.1 With the help of the support circuit, the accelerator pedal successfully generated 0-5
V for idle and WOT positions, respectively.
79
Figure 7.2 The motor encoder was tested for a small motor and it generated square wave
outputs.
Figure 7.3 The current sensor IC was also tested. It was a bidirectional sensor and as expected,
it produced half of its power supply for zero current.
80
Also the whole control circuit was designed in Ultiboard. It was another time-consuming, pain
staking process because-
most of the components’ foot prints were not available in the library.
the whole control circuit could not be designed in one single board because the PCB
machine available in the lab could only produce PCB boards of size 9cm x 9 cm. Thus
the whole board had to be split in four small boards and the students had to be extremely
meticulous to make sure the interconnections between them were correct.
The chief reason for the failure to produce a working prototype was the unavailability of an in-
circuit programmer. In-circuit programmer is a programmer that allows the compiled firmware to
be downloaded in the micro-controller while keeping it in the breadboard. The programmer that
was available in the lab was PICStartPlus. The programmer set up is shown in Figure 7.4.
Figure 7.4 The PICStartPlus Programmer.
Whenever code is developed for an embedded system, it is developed in chunks. The developed
portion is then compiled, simulated and tested. The code developer writes further codes only if
the simulation and testing are successful for previously developed codes. For this project, when
the code was being developed, the students could only simulate the code as they did not have
81
micro-controller chip at that time. When the students finally got their hands on the micro-
controller, the unavailability of an in-circuit programmer hindered the testing of the code. The
simulation circuit was built in the breadboard but to test the code in portions, the micro-
controller had to be shuttled between the breadboard and PICStartPlus. It made the testing almost
close to impossible as putting the micro-controller into the breadboard and PICStartPlus back
and forth was damaging for its DIP pins.
Despite not being able to test the firmware step by step, a prototype motor drive was built and is
shown in Figure 7.5. The whole compiled firmware was downloaded in the micro-controller chip
with the hope that it might work, but the system did not work at the end.
Figure 7.5 Product prototype.
7.2 Future Work Recommendations
Since the theoretical design and simulation has been done successfully, this project presents a
wonderful opportunity to build a working motor drive that would allow motoring and
82
regeneration both in forward and reverse directions. If someone wants to go ahead and build
such a motor drive, the following recommendations would be useful.
Construction of a successful motor drive will be an enormous task. If a project is
undertaken such that the motor drive be built as part of a senior year design project
following the design presented in this report, a full and thorough understanding of the
design and simulation documented in this report is a must. The construction of a working
motor drive would require many stages of testing and design and therefore, more than a
month cannot be spent in studying this report and doing other literature survey.
EMC issues are of great importance. This report talks very briefly about this issue. To
build a motor controller that is robust in the presence of high level (this high level has to
be quantified) of noise, more research has to be done regarding EMC and noise
immunity.
An in-circuit programmer must be used to download and test the firmware in the micro-
controller.
If regeneration current leads to over-voltage in the battery, a flywheel or a super capacitor
may be used to store the regenerated energy.
To prevent overheating in the motor, a temperature sensor could be installed. This sensor
will provide temperature feedback to the micro-controller. If the temperature crosses the
maximum set limit, the micro-controller will the automatically shut down the system.
Initially, it was also planned that a voltmeter and speedometer would be built for the car.
These systems could be built very easily. Micro-controller already has the speed feedback
and battery voltage feedback data. Doing some little programming, the micro-controller
could be made to display the voltage and speed in seven segment displays.
Through hole (DIP) micro-electronic components must be ordered should they are
available. The through hole components are much easier to solder than surface mount
(SOIC) components.
83
WORKS CITED
[1] This image is available at: http://www.evsource.com/conversion/documents/pdr/PDR_200sx.pdf [Accessed: Jan. 10, 2010]
[2] Mehrdad Ehsani, Yimin Gao, Sebastien E. Gay, Ali Emadi, Modern Electric, Hybrid Electric and Fuel Cell Vehicles. Florida: Boca Raton, FL : 2000 N.W. Corporate Blvd / CRC Press LLC, page 101-102.
[3] Rui Santos, Fernando Pais, Carlos Ferreira, Hugo Ribeiro, Pedro Matos. Electric Vehicles-Design and Implementation Strategies of Power Train. Escola Superior de Tecnologia do Instituto Politécnico de Tomar – Quinta do Contador – Estrada da Serra, 2300 Tomar, Portugal.
[4]-[12] Formula Hybrid 2010 Competition Rules Available: http://www.formula-hybrid.org/rules.php [Accessed: Sep. 15, 2010]
[13], [15] James Larmine, John Lowry, Modern Electric, Electric Vehicles Technology Explained. Sussex, England: John Wiley & Sons Ltd, page1 42-150.
[14] This image is available at: http://en.wikipedia.org/wiki/Fleming%27s_left_hand_rule_for_motors [Accessed: April. 10, 2010]
[16] Iqbal Husssain, Electric and Hybrid Vehicles Design Fundamentals. Boca Raton, Florida: CRC Press, pg. 99.
[17]-[18] Stephen J. Chapman, Electric Machinery Fundamentals. New York: McGraw Hills, pg. 559-561.
[19], [22] James Larmine, John Lowry, Modern Electric, Electric Vehicles Technology Explained. Sussex, England: John Wiley & Sons Ltd, page 183-212.
[20] This image is available at: http://lh5.ggpht.com/_vHwtYfzMc9c/SpYtri6kcTI/AAAAAAAAARs/9ehLZMGcOxo/Slide1_thumb%5B7%5D.jpg [Accessed: April. 10, 2010]
84
[21] This image is available at: http://www.newkellycontroller.com/index.php?cPath=21_63 [Accessed: April. 10, 2010]
[22] Formula Hybrid International Competition Available: http://cavt.eng.ua.edu/Files/SAE_hybrid_09_Program.pdf [Accessed: Dec. 3, 2009]
[23] V. R. Moorthi, Power Electronics: Devices, Circuits and Applications, 3rd Edition. India: Oxford University Press, 2006, pp 300-306.
[24] Ali Emadi, Handbook of automotive power electronics and motor drives. Florida: Boca Raton, FL : Taylor & Francis/CRC Press, 2005, Ch 6, section 6.2.
[25] Vrej Barkhordarian, “Power MOSFET Basics” International Rectifier. [pdf]. Available: http://www.irf.com/technical-info/appnotes/mosfet.pdf [Accessed: Apr. 1, 2010].
[26] S Davis, “Power-MOSFET Gate Drivers”, Electronic Design Archive.[pdf]. Available: http://www.elecdesign.com/Files/29/8415/8415_01.pdf [Accessed: Apr. 1, 2010].
[27] “Pre-charge Circuit”. [Online]. Available: http://liionbms.com/php/precharge.php [Accessed: Apr. 3, 2010].
[28] This image is available at: http://en.wikipedia.org/wiki/Pre-charge [Accessed: Apr. 10, 2010]
[29] This image is available at: http://commons.wikimedia.org/wiki/File:Hall_effect.gif [Accessed: Apr. 10, 2010]
[30] “Hall current sensing”. [Online]. Available: http://machinedesign.com/article/sensor-sense-hall-effect-current-sensors-0809 [Accessed: Apr. 3, 2010].
[31]-[33] Dean Thompson, “A Four Quadrant Adjustable Speed Drive For Series Wound DC Motors”, University of Southern Queensland, Queensland, Australia, Final Year Project Rep. 2003/04.
[34]-[35] Muhammad H Rashid, Power Electronics: Circuits, Devices and Applications, 3rd.
85
NJ: Pearson, pg. 827-830.
[36]-[37] Rudy Stevens, “DESIGN OF SNUBBERS FOR POWER CIRCUITS”. [pdf]. Available: http://www.cde.com/tech/design.pdf [Accessed: Mar. 10, 2010]
[38] Richard Valentine, Motor Control Electronics Handbook. NY: McGraw Hill, pg.225-235.
[39] “Successive approximation conversion”. [online] Available: http://www.microlink.co.uk/a-d.html [Accessed: Mar. 10, 2010]
[40] This image is available at: http://www.mikroe.com/en/books/pic-books/mikroc/ch3/ [Accessed: Apr. 10, 2010]
[41]-[45] Matin Bates, Programming 8-bit PIC microcontrollers in C [electronic resource] : with interactive hardware simulation. Amsterdam ; Boston, Mass. : Elsevier/Newnes, c2008, pg 9-11.
[46]-[47] James Larmine, John Lowry, Modern Electric, Electric Vehicles Technology Explained. Sussex, England: John Wiley & Sons Ltd, page 24-45.
86
APPENDIX 1. Project Management & Earned Value Spreadsheet
Budgeted Time of Work Scheduled, TAMUQ HIP Project 2010
Wk =Week
Wk 1
Wk 2
Wk 3
Wk 4
Wk 5
Wk 6
Wk 7
Wk 8
Wk 9
Wk 10
Wk 11
Wk 12
10-Jan
18-Jan
26-Jan
3-Feb
11-Feb
19-Feb
27-Feb
7-Mar
15-Mar
23-Mar
31-Mar
8-Apr
SL Task Name Time Budget
17-Jan
25-Jan
2-Feb
10-Feb
18-Feb
26-Feb
6-Mar
14-Mar
22-Mar
30-Mar
7-Apr
15-Apr
1 Literature Survey 24 24
2 Motor Sizing and Simulation 24 24
3 Battery Sizing and Simulation 24 24
4 Project Proposal 24 24
5
Controller topology selection-semiconductor realization 10 10
6 Switches selection and power loss calculation 30 30
7 reactive component selection 15 15
8
State space modeling/averaged equivalent circuit 20 20
9 Frequency response, TF, small signal analysis 20 20
10 Simulation by Simulink 20 20
11 Micro-controller programming 60 60
12 Prototype design 60 30 30
13 Testing 30 30
14 Finish report 15 15
15 Prepare PPT and poster 10 10
Weekly Total Budgeted 386 24 24 48 40 35 40 60 30 30 30 15 10
Cumulative BTWC 24 48 96 136 171 211 271 301 331 361 376 386
Budgeted Time of Work Performed & Actual Time of Work Performed, TAMUQ HIP Project 2010
Wk 1
Wk 2
Wk 3
Wk 4
Wk 5
Wk 6
Wk 7
Wk 8
Wk 9
Wk 10
Wk 11
Wk 12
Wk =Week 10-Jan
18-Jan
26-Jan
3-Feb
11-Feb
19-Feb
27-Feb
7-Mar
15-Mar
23-Mar
31-Mar 8-Apr
SL Task Name Time Budget
17-Jan
25-Jan
2-Feb
10-Feb
18-Feb
26-Feb
6-Mar
14-Mar
22-Mar
30-Mar 7-Apr
15-Apr
1 Literature Survey 35 35
45 45
2 Motor Sizing and Simulation 35 35
87
30 30
3 Battery Sizing and Simulation 35 35
40 40
4 Project Proposal 35 35
33 33
5
Controller topology selection-semiconductor realization 20 20
30 30
6
Switches selection and power loss calculation 40 40
35 35
7
reactive component selection 15 15
30 30
8
State space modeling/averaged equivalent circuit 35 35
20 20
9
Study the Architecture of PIC 16F877A 30 30
25 25
10
Learn C Programming and Use of Proteus VS< 35 35
40 40
11 Micro-controller programming 85 85
100 100
12 Prototype design 90 45 45
77 37 40
13 Testing 68 23 45
100 40 60
14 Finish report 25 25
20 20
15 Prepare PPT and poster 20 20
20 20
Weekly BTWP 603 35 35 70 60 50 65 85 45 68 45 25 20
Cumulative BTWP 35 70 140 200 250 315 400 445 513 558 583 603
Weekly ATWP 45 30 73 65 50 65 100 37 80 60 20 20
Cumulative ATWP 45 75 148 213 263 328 428 465 545 605 625 645
SV 11 22 44 64 79 104 129 144 182 197 207 217
88
CV -10 -5 -8 -13 -13 -13 -28 -20 -32 -47 -42 -42
BAC 24 48 96 136 171 211 271 301 331 361 376 386
EAC 30.9 51.4 101.5 144.8 179.9 219.7 290.0 314.5 351.6 391.4 403.1 412.9
VAC -6.9 -3.4 -5.5 -8.8 -8.9 -8.7 -19.0 -13.5 -20.6 -30.4 -27.1 -26.9
Comments:
There is huge difference between the budgeted time of word scheduled and budgeted time/actual time of work performed. Most of the tasks required more time than we expected as we had to self-train ourselves before doing the actual work. For example, before working with the micro-controller, we first had to study its architecture and the programming language.
-50
0
50
100
150
200
250
300
350
400
450
0 2 4 6 8 10 12 14
Time Vs CV, BAC, SV, EAC, VAC
CV
SV
BAC
EAC
VAC
89
Keeping track of this project management chart and earned value spreadsheet was hard as both them were very complex. We propose next year students to adopt a simpler project management method.
90
APPENDIX 2. Matlab Code
function dvdt=ODEfsaeacc(t,v)
% Inputs to the function G=2; %Gear Ratio r=0.25; %radius of the tire in meters urr=0.075; % Friction coefficient of the tire m = 500; % Mass of the vehicle including driver in kg g = 9.81; % Gravitational constant in m/s2 ro=1.25; % Density of the air in kg/m3 Cd= 0.75; %aero-dynamic drag co-efficient A=0.4; %Frontal area of the car in m2 theta = 0; %Slpoe angle in radians sc=45; %Speed constant of the motor in rpm/V Ra=0.01675; %Armature resistance in Ohms Es=84; %Supply voltage of the motor RP=14390; %Rated power in watt ng=0.9; % Efficiency %+++++++++++Setting Up the Equation++++++++++++ kphi=60/(2*pi*sc); %calculates kphi T0=kphi*Es/Ra; k=(kphi^2)/Ra; dvdt=((ng*RP/v)-urr*m*g-0.5*ro*A*(v^2)-m*g*sin(theta))/m; v0=0.001; tspan=0:0.5:25; [t,v]=ode45('ODEfsaeacc',tspan,v0); for i=1:length(v) if v(i)>22.2222; v(i)= 22.2222; else v(i)=v(i); end; end; plot (t,v*3.6)
91
APPENDIX 3. Firmware Code
1: '++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++' 2: 'Program for 4-Quadrant PMDC MOTOR Control 3: 'Power Train Design of TAMUQ Formula Hybrid in Progress Car 4: 'Date: March 7, 2010 5: 'Program Written by Mahmudul Alam 6: '++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++' 7: 8: 9: program OPTIM 10: 11: '--------------------------------- 12: 'Declaring Miscellaneous Variables 13: '--------------------------------- 14: dim tmp, acc ,brk, ilim, spdfeed, batv as word 15: 16: '------------------------------------ 17: ' Lcd module connections declarations 18: '------------------------------------ 19: dim LCD_RS as sbit at RD7_bit 20: LCD_EN as sbit at RD6_bit 21: LCD_D4 as sbit at RD5_bit 22: LCD_D5 as sbit at RD4_bit 23: LCD_D6 as sbit at RD3_bit 24: LCD_D7 as sbit at RD2_bit 25: 26: LCD_RS_Direction as sbit at TRISD7_bit 27: LCD_EN_Direction as sbit at TRISD6_bit 28: LCD_D4_Direction as sbit at TRISD5_bit 29: LCD_D5_Direction as sbit at TRISD4_bit 30: LCD_D6_Direction as sbit at TRISD3_bit 31: LCD_D7_Direction as sbit at TRISD2_bit 32: '------------------- 33: 'Program Subroutines 34: '------------------- 35: '------------------------------ 36: 'Subroutine 1: Shutdown System 37: '------------------------------ 38: sub procedure Shut_Down 39: PWM1_Stop 'Stop PWM Signal 1 40: PWM2_Stop 'Stop PWM Singnal 2 41: PORTC=0 'Turn off all power stage signals 42: lcd_out(1, 1, "System Shutdown") 'Display shutdown message 43: while TRUE 'System Shutdown in an endless loop 44: wend 45: end sub 46: 47: '----------------------------------------- 48: ' Sub-routine 2: PWM Module Initialization 49: '----------------------------------------- 50: sub procedure InitPWM() 51: PORTC = 0 ' Clear PORTC Pins 52: TRISC = 0 ' Configure PORTC pins as output 53: PWM1_Init(1000) ' Initialize PWM1 module at 15KHz
92
54: PWM2_Init(1000) ' Initialize PWM2 module at 15KHz 55: end sub 56: 57: '------------------------------------ 58: ' Sub-routine 3: Capacitor Precharge 59: '------------------------------------ 60: sub procedure Precharge 61: tmp=0 'Initially count i = 0 62: while tmp < 15 'Give 15 seconds for capacitor to reach within 45V 63: tmp = tmp + 1 'Timer incrementing 64: wend 65: 66: if adc_read(6) > 960 then 67: lcd_out(1,1, "Cap Charged") 68: else 69: lcd_out(1,1, "Precharge Fault") 70: Shut_Down() 71: end if 72: end sub 73: 74: sub procedure Initial_Direction_Check 75: InitPWM() 76: PWM2_Start() 77: PWM2_Set_Duty(255) 'Set duty cycle of PWM2 to 100% 78: tmp=PORTB.2 'Read direction switch position 79: 80: if tmp=1 then 81: lcd_out(1, 1, "Reverse Mode ") 82: PORTC.5=1 'MOSFET Q3 is turned on 83: PORTC.6=0 'MOSFET Q4 is turned off 84: else 85: lcd_out(1, 1, "Forward Mode ") 86: delay_ms(1000) 87: PORTC.5=0 'MOSFET Q3 is turned off 88: PORTC.6=1 'MOSFET Q4 is turned on 89: end if 90: end sub 91: 92: 93: '----------------------------------------------------------------------' 94: 'This is the main program loop' 95: '-----------------------------------------------------------------------' 96: 97: main: 98: intcon=0 'Interrupts Disabled 99: 100: 'Initializing Port D 101: PORTD = 0 'Clear Port D pins 102: TRISD = 0 'Port D pins configured as output 103: 104: 'Initializing Port C 105: PORTC = 0 'Clear Port C pins 106: TRISC = 0 'Port C pins configured as output 107: 108: 'Initializing LCD Screen
109: Lcd_Init() 'Call initialize LCD sub-routine
93
110: Lcd_Cmd(_LCD_CLEAR) 'Clear display of LCD Screen 111: Lcd_Cmd(_LCD_CURSOR_OFF) 'LCD Cursor off 112: lcd_out(1, 1, "Welcome! (c)Alam") 'LCD Output shows the program name 113: lcd_out(2, 1, "Please wait! ") 114: Lcd_Cmd(_LCD_CLEAR) 115: 'Initializing PWM Signals 116: InitPWM() 'Call initialize PWM sub-routine 117: 118: 'Initializing Port B 119: PORTB=0 'Clear Port C pins 120: TRISB=1 'Port B pins configured as input 121: 122: 'Initializing all Analogue to Digital (ADC) inputs in Port A and Port E 123: 124: ADCON1 = %10000000 'Configure analog inputs and Vref 125: TRISA= %11111111 'Port A is input 126: TRISE= %00000111 'Port E is input 127: 128: 129: asm 130: CLRWDT 'Clears watch dog timer 131: end asm 132: Precharge () 133: Initial_Direction_Check() 134: 135: while PORTB.1<>1 'As long as power stage is not enabled 136: Lcd_Cmd(_LCD_CLEAR) 'Clear LCD Screen 137: lcd_out(1, 1, "Enable PW STG") 'Prompt to driver to enable power stage 138: 139: wend 140: Lcd_Cmd(_LCD_CLEAR) 141: lcd_out(1, 1, "PS Enabled") 142: big_loop: 143: While TRUE 144: 145: '______________________________________________________________ 146: 'Check battery voltage, shut down system if it is outside the range 147: 148: if ADC_Read(4) > 1023 then 'If supplied voltage > 48V, system shut down 149: lcd_out(1, 1, "Bat Voltage High") 150: Shut_down() 151: end if 152: 153: if ADC_Read(4) < 512 then 'If supplied voltage > 48V, system shut down 154: lcd_out(1, 1, "Bat Voltage Low") 155: 156: Shut_down() 157: end if 158: '_____________________________________________________________________ 159: 'Check direction by calling direction subroutine 160: if PORTB.2 <> tmp then 161: tmp=PORTB.2 162: PWM1_Set_Duty(0) 163: PORTC.3=0 'HI side off 164: PORTC.4=0 'Low side off 165: 'LCD will show that the motor is spinning down 166: lcd_out(1, 1, "Spinning down...")
94
167: 168: while adc_read(5) > 20 169: wend 170: Initial_Direction_Check() 171: end if 172: 'Read parameters from ADC channels and store them in appropriate variables 173: acc=adc_read(0) 174: brk=adc_read(1) 175: ilim = adc_read(2) 176: batv=ADC_Read(4) 177: spdfeed = adc_read(5) 178: PWM1_Start() 179: '___________________________________________________________________________ 180: 181: if tmp = 1 then 182: goto REV 183: else if tmp =0 then 184: goto FWD 185: end if 186: end if 187: goto Skip 188: '___________________________________________________________________________ 189: FWD: 190: 'Break or Acceleration ADC will never read 0 as their will be some noise 191: if brk >= 20 then 192: goto Forward_Regen 193: end if 194: 195: if acc >= 20 then 196: goto Forward_Motoring 197: end if 198: 199: Forward_Regen: 200: lcd_out(1,1, "FWD Regen :)") 201: if (ilim <= 324) and (batv >= 768) then 202: goto Skip 203: end if 204: brk=brk/4 205: PWM1_Set_Duty(brk) 206: PORTC.3=0 207: PORTC.4=1 208: goto big_loop 209: 210: Forward_Motoring: 211: lcd_out(1,1, "FWD Mot :)") 212: if (ilim >= 1012) then 213: goto Skip 214: end if 215: PORTC.3=1 216: PORTC.4=0 217: acc= acc/4 218: PWM1_Set_Duty(acc) 219: goto big_loop 220:
95
221: REV: 222: if brk >= 20 then 223: goto Reverse_Regen 224: end if 225: 226: if acc >= 20 then 227: goto Reverse_Motoring 228: end if 229: 230: goto Skip 231: 232: Reverse_Motoring: 233: lcd_out(1, 1, "REV Mot :)") 'LCD Output 234: 235: if (ilim <= 0) then 236: goto Skip 237: end if 238: acc= acc/4 239: PWM1_Set_Duty(acc) 240: PORTC.3=0 241: PORTC.4=1 242: goto big_loop 243: 244: Reverse_Regen: 245: lcd_out(1, 1, "REV Regen :)") 'LCD Output 246: if (ilim >= 668) and (batv > 768) then 247: goto Skip 248: end if 249: brk=brk/4 250: PWM1_Set_Duty(brk) 251: PORTC.3=1 252: PORTC.4=0 253: 254: Skip: 255: PORTC.3=0 256: PORTC.4=0 257: wend 258: end.
96
APPENDIX 4. Circuit Diagram
97
98
APPENDIX 5. Bill of Materials
This bill of material refers to the components of the circuit diagram given in Appendix 4 by means of component values.
Value Manufacturer Manufacture Part Number Supplier Supplier
Part No. Unit Cost
Quan-tity Total
100u Panasonic - ECG ECE-A1CKA101 Digikey P833-ND $0.15 5 $0.75
10n Panasonic - ECG ECJ-0EB1E103K Digikey PCC2270TR-ND $0.00 5 $0.02
100n Yageo CX0805MRX7R7BB104 Digikey 311-1245-1-ND $1.29 3 $1.01
0.1u Vishay/BC
Components K104Z15Y5VE5TH5 Digikey BC1154TR-ND $0.02 15 $0.33
20p Cornell Dubilier
Electronics (CDE) MC08EA200J-F Digikey 338-1101-ND $1.09 4 $4.36
1u TDK Corporation C3216X8R1E105K Digikey 445-2517-2-ND $0.11 10 $1.08
15000 Cornell Dubilier
Electronics (CDE) 3186BC153M060BPA1 Digikey 3186BC153M060BPA1-
ND $21.58 1 $21.58
10n Murata Electronics
North America GRM033R70J103KA01D Digikey 490-1262-2-ND $0.00 10 $0.04
1500u Nichicon PCJ0G152MCL1GS Digikey 493-3036-2-ND $1.00 3 $35.03
33V Micro Commercial Co
1N5364B-TP Digikey 1N5364BTPMSTR-ND $0.15 3 $0.44
20V ON Semiconductor
1N5357BRLG Digikey 1N5357BRLGOSCT-ND $0.46 4 $1.84
3.3 V Diodes Incr 1N5226B-T Digikey 1N5226BDITR-ND $0.04 15 $6.90
15V ON
Semiconductor BZG03C15G Digikey BZG03C15GOSTR-ND $0.12 10 $3.60
13 V ON Semiconductor
1N5350BRLG Digikey 1N5350BRLGOSCT-ND $0.46 3 $1.38 5.6 V Diodes Inc 1N5232B-T Digikey 1N5232BDITR-ND $0.04 3 $0.44
5V ON
Semiconductor 1N5350BRLG Digikey 1N5350BRLGOSCT-ND $0.46 2 $0.92
NA US Digital Products E2-32-079-I-D-D-B
US Digital
Products E2-32-079-I-D-D-B $62.31 1 $62.31
NA US Digital Products CA-C5-W5-NC-1
US Digital
Products CA-C5-W5-NC-1 $5.75 1 $5.75 4A Bourns Inc. SF-1206F400-2 Digikey SF-1206F400-2TR-ND $0.34 3 $1.02
175 A Littelfuse Inc 0298175.ZXEH Digikey F3325-ND $7.26 1 $7.26
100u JW Miller A Bourns Company
2312-H-RC Digikey M8838-ND $3.99 1 $3.99
298.39u Coiltronics/Div of Cooper/Bussmann CTX300-3P-R Digikey CTX300-3P-R-ND $1.89 2 $3.78
Mars Etek-R Cloud
Electric MO-ME-0708 $434.00 1 $434.00
20MHz NDK
NX5032GA 20MHZ AT-W Digikey 644-1136-2-ND $0.64 3 $1.91
NA IXYS IXTH250N075T Digikey IXTH250N075T-ND $5.18 6 $31.08
Shunt Vishay/Dale WSL2010R4000FEA Digikey WSLE-.40TR-ND $0.34 5 $1.68
0.68 Yageo FMP200JR-52-0R68 Digikey 0.68ZTR-ND $0.08 10 $0.82
NA Allegro
Microsystems Inc
ACS756SCA-100B-PFF-T Digikey 620-1238-ND $6.44 1 $6.44
NA APEM
Components 5636ABX814 Digikey 5636ABX814-ND $8.40 2 $16.80
NA NKK Switches of
America Inc G3T12AP-RO Digikey 360-1774-ND $5.20 4 $20.80 NA National LM2576S-12/NOPB Digikey LM2576S-12-ND $3.44 2 $6.88
99
Semiconductor
NA Fairchild Semiconductor
LM7805CT Digikey LM7805CT-ND $0.43 2 $0.86
NA Microchip
Technology PIC16F877A-I/P Digikey PIC16F877A-I/P-ND $6.72 4 $26.88
NA
Mill-Max Manufacturing
Corp. 214-44-640-01-670800 Digikey ED90244-ND $3.98 1 $3.98
NA STMicroelectronics TL431CZT Digikey 497-8191-2-ND $0.20 2 $0.40
STMicroelectronics 74V2G00STR Digikey 497-1298-2-ND $0.21 3 $0.64
NA Maxim Integrated
Products MAX4081SASA+ Digikey MAX4081SASA+-ND $1.24 1 $1.24
NA National
Semiconductor LM5101AM/NOPB Digikey LM5101AM-ND $3.61 3 $10.83
NA National
Semiconductor LM2917M-8/NOPB Digikey LM2917M-8-ND $2.02 2 $4.04
NA ON
Semiconductor NSS12500UW3T2G Digikey NSS12500UW3T2GOSTR-
ND $0.36 5 $1.24
NA Assmann
Electronics Inc H7MXH-2506M Digikey H7MXH-2506M-ND $3.68 1 $3.68
NA Norcomp Inc. 190-009-163R001 Digikey 190-09MA-ND $3.17 1 $3.17
16x2 Ebay HD44780 Ebay HD44780 $7.29 1 $7.29
NA TDK-LAMBDA
AMERICAS INC ZUP/NC401 Digikey 285-1666-ND $37.13 1 $37.13
NA Maxim Integrated
Products MAX232EPE+ Digikey MAX232EPE+-ND $3.98 1 $3.98
NA Tyco Electronics 1986242-2 Digikey A99381-ND $6.75 3 $20.25 TOTAL $743.37
100
APPENDIX 6. Filter Inductor and Capacitor Selection Calculations
101
102
103
104
105
106
107
108
109
110
111
112
113
114
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APPENDIX 7. Report Attachment
The CD attached with this report contains the following items:
A soft copy of the report. Project proposal. Mikrobasic file of the source code. The Proteus VSM file of the control circuit. The circuit diagram drawn on A3 sheet. A video recorded by the students that shows how the motor encoder was tested. Project Presentation. MATHCAD file of filter capacitor/inductor calculations Project Poster.
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APPENDIX 8. Student Biography
Mahmudul Alam
Mahmudul Alam is an electrical engineering senior at Texas A&M University at Qatar. He came to Qatar in 1993 and since then he has been living here. He graduated from a community school named Bangladesh MHM School and College prior to his admission at A&M. During his high school life, Alam was selected as the games prefect of the school. During his time at A&M, Alam served as the secretary of TAMUQ IEEE student chapter and was an active member of Aggie Cricket Club. He successfully completed an undergraduate research project titled Energy Saving by Power factor correction and its Application to the Industries of Qatar. The project surveyed the power factor conditions in an industrial substation. Alam’s professional interests include: power electronics, dc-dc converter, embedded systems design, math, statistics, engineering ethics and engineering economics.
Aside from academics, Alam is interested in cooking, reading, watching cricket, discussing Islamic theology, internet surfing and watching cartoons.
Jaber Al-Marri
Jaber Al-Marri is also an electrical engineering senior at Texas A&M University at Qatar. Before admission at A&M, he graduated from Qatar Scientific School. Upon graduation from A&M, he will be working in Qatar Petroleum, his sponsor. Besides working, he also plans to open his own engineering consultation firm. Jaber is great soccer fan.